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A library of dependency-free JavaScript utilities that do just one thing.

anguscroll.com/just

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Just

Docs | Why? | Try It | Contribute!

A library of zero-dependency npm modules that do just one thing. A guilt-free alternative to those bulkier utility libraries. Ideal for PWA development or whenever bytes are precious.

We welcome contributions. Please follow our contribution guidelines.

Try 🍦

A REPL for every utility (powered by RunKit)

Read 📚

TRADEOFFS.md -- When to use Just (and when not to).
The Zen of Dependency-Free -- Why I wrote Just.

ES and CJS modules available for every utility

All packages support ES module or Common JS syntax without requiring transpilation

// esm (node / bundler)
import clone from 'just-clone';

// esm (native browser code)
import clone from './node_modules/just-clone/index.mjs';

// cjs
const clone = require('just-clone');

TypeScript

We've now added TypeScript definitions and tests for every Just utility

Browser/Platform Support 💻

Most utilities still work with any platform that supports ES5, but these are the earliest versions guranteed to support every utility. For guidance, any platform that supports spread in array literals will work with Just.

Chrome	Safari	Firefox	Edge	Node	Mobile Safari	Android Chrome
46	8	16	12	6.0	8	46

The Modules 📦

Collections

just-diff

npm install just-diff

yarn add just-diff

Return an object representing the difference between two other objects Pass converter to format as http://jsonpatch.com

import {diff} from 'just-diff';

const obj1 = {a: 4, b: 5};
const obj2 = {a: 3, b: 5};
const obj3 = {a: 4, c: 5};

diff(obj1, obj2);
[
  { "op": "replace", "path": ['a'], "value": 3 }
]

diff(obj2, obj3);
[
  { "op": "remove", "path": ['b'] },
  { "op": "replace", "path": ['a'], "value": 4 }
  { "op": "add", "path": ['c'], "value": 5 }
]

// using converter to generate jsPatch standard paths
import {diff, jsonPatchPathConverter} from 'just-diff'
diff(obj1, obj2, jsonPatchPathConverter);
[
  { "op": "replace", "path": '/a', "value": 3 }
]

diff(obj2, obj3, jsonPatchPathConverter);
[
  { "op": "remove", "path": '/b' },
  { "op": "replace", "path": '/a', "value": 4 }
  { "op": "add", "path": '/c', "value": 5 }
]

// arrays
const obj4 = {a: 4, b: [1, 2, 3]};
const obj5 = {a: 3, b: [1, 2, 4]};
const obj6 = {a: 3, b: [1, 2, 4, 5]};

diff(obj4, obj5);
[
  { "op": "replace", "path": ['a'], "value": 3 }
  { "op": "replace", "path": ['b', 2], "value": 4 }
]

diff(obj5, obj6);
[
  { "op": "add", "path": ['b', 3], "value": 5 }
]

// nested paths
const obj7 = {a: 4, b: {c: 3}};
const obj8 = {a: 4, b: {c: 4}};
const obj9 = {a: 5, b: {d: 4}};

diff(obj7, obj8);
[
  { "op": "replace", "path": ['b', 'c'], "value": 4 }
]

diff(obj8, obj9);
[
  { "op": "replace", "path": ['a'], "value": 5 }
  { "op": "remove", "path": ['b', 'c']}
  { "op": "add", "path": ['b', 'd'], "value": 4 }
]

just-diff-apply

npm install just-diff-apply

yarn add just-diff-apply

Apply a diff object to an object. Pass converter to apply a http://jsonpatch.com standard patch

  import {diffApply} from 'just-diff-apply';

  const obj1 = {a: 3, b: 5};
  diffApply(obj1,
    [
      { "op": "remove", "path": ['b'] },
      { "op": "replace", "path": ['a'], "value": 4 },
      { "op": "add", "path": ['c'], "value": 5 }
    ]
  );
  obj1; // {a: 4, c: 5}

  const obj2 = {a: 3, b: 5};
  diffApply(obj2,
    [
      { "op": "move", "from": ['a'], "path": ['c']},
    ]
  );
  obj2; // {b: 5, c: 3}

  // using converter to apply jsPatch standard paths
  // see http://jsonpatch.com
  import {diffApply, jsonPatchPathConverter} from 'just-diff-apply'
  const obj3 = {a: 3, b: 5};
  diffApply(obj3, [
    { "op": "remove", "path": '/b' },
    { "op": "replace", "path": '/a', "value": 4 }
    { "op": "add", "path": '/c', "value": 5 }
  ], jsonPatchPathConverter);
  obj3; // {a: 4, c: 5}

  // arrays (array key can be string or numeric)
  const obj4 = {a: 4, b: [1, 2, 3]};
  diffApply(obj4, [
    { "op": "replace", "path": ['a'], "value": 3 }
    { "op": "replace", "path": ['b', 2], "value": 4 }
    { "op": "add", "path": ['b', 3], "value": 9 }
  ]);
  obj4; // {a: 3, b: [1, 2, 4, 9]}

  // nested paths
  const obj5 = {a: 4, b: {c: 3}};
  diffApply(obj5, [
    { "op": "replace", "path": ['a'], "value": 5 }
    { "op": "remove", "path": ['b', 'c']}
    { "op": "add", "path": ['b', 'd'], "value": 4 }
  ]);
  obj5; // {a: 5, b: {d: 4}}

just-compare

npm install just-compare

yarn add just-compare

Compare two collections

import compare from 'just-compare';

// primitives: value1 === value2
// functions: value1.toString == value2.toString
// arrays: if length, sequence and values of properties are identical
// objects: if length, names and values of properties are identical
compare([1, [2, 3]], [1, [2, 3]]); // true
compare([1, [2, 3], 4], [1, [2, 3]]); // false
compare({a: 2, b: 3}, {a: 2, b: 3}); // true
compare({a: 2, b: 3}, {b: 3, a: 2}); // true
compare({a: 2, b: 3, c: 4}, {a: 2, b: 3}); // false
compare({a: 2, b: 3}, {a: 2, b: 3, c: 4}); // false
compare([1, [2, {a: 4}], 4], [1, [2, {a: 4}]]); // false
compare([1, [2, {a: 4}], 4], [1, [2, {a: 4}], 4]); // true
compare(NaN, NaN); // true

just-clone

npm install just-clone

yarn add just-clone

Deep copies objects, arrays, maps and sets

// Deep copies objects and arrays, doesn't clone functions

import clone from 'just-clone';

var arr = [1, 2, 3];
var subObj = { aa: 1 };
var obj = { a: 3, b: 5, c: arr, d: subObj };
var objClone = clone(obj);
arr.push(4);
objClone.d.bb = 2;
obj; // {a: 3, b: 5, c: [1, 2, 3, 4], d: {aa: 1}}
objClone; // {a: 3, b: 5, c: [1, 2, 3], d: {aa: 1, bb: 2}}

just-pluck-it

npm install just-pluck-it

yarn add just-pluck-it

Pluck a property from each member of a collection

import pluck from 'just-pluck-it';

pluck([{a:1, b:2}, {a:4, b:3}, {a:2, b:5}], 'a'); // [1, 4, 2]
pluck({x: {a:1, b:2}, y: {a:4, b:3}, z: {a:2, b:5}}, 'a'); // {x: 1, y: 4, z: 2}

just-flush

npm install just-flush

yarn add just-flush

Returns a copy of an array or object with null/undefined members removed

import flush from 'just-flush';

flush([1, undefined, 2, null, 3, NaN, 0]); // [1, 2, 3, NaN, 0]
flush([true, null, false, true, [null], undefined]); // [true, false, true, [null]]
flush({a: 2, b: null, c: 4, d: undefined}); // {a: 2, c: 4}
flush('something'); // undefined
flush(); // undefined

Objects

just-extend

npm install just-extend

yarn add just-extend

Extend an object

import extend from 'just-extend';

var obj = {a: 3, b: 5};
extend(obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 4, b: 5, c: 8}

var obj = {a: 3, b: 5};
extend({}, obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 3, b: 5}

var arr = [1, 2, 3];
var obj = {a: 3, b: 5};
extend(obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push(4);
obj; // {a: 3, b: 5, c: [1, 2, 3, 4]}

var arr = [1, 2, 3];
var obj = {a: 3, b: 5};
extend(true, obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push(4);
obj; // {a: 3, b: 5, c: [1, 2, 3]}

extend({a: 4, b: 5}); // {a: 4, b: 5}
extend({a: 4, b: 5}, 3); {a: 4, b: 5}
extend({a: 4, b: 5}, true); {a: 4, b: 5}
extend('hello', {a: 4, b: 5}); // throws
extend(3, {a: 4, b: 5}); // throws

just-merge

npm install just-merge

yarn add just-merge

Shallow assign. Like just-extend but without deep copy option.

import merge from 'just-merge';

let obj = {a: 3, b: 5};
merge(obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 4, b: 5, c: 8}

let obj = {a: 3, b: 5};
merge({}, obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 3, b: 5}

let arr = [1, 2, 3];
let obj = {a: 3, b: 5};
merge(obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push[4];
obj; // {a: 3, b: 5, c: [1, 2, 3, 4]}

merge({a: 4, b: 5}); // {a: 4, b: 5}
merge(3, {a: 4, b: 5}); // throws
merge({a: 4, b: 5}, 3); // throws
merge({a: 4, b: 5}, {b: 4, c: 5}, 'c'); // throws

just-values

npm install just-values

yarn add just-values

Return property values as an array

const values = require('just-values');

values({a: 4, c: 8}); // [4, 8]
values({a: {aa: 2}, b: {bb: 4}}); // [{aa: 2}, {bb: 4}]
values({}); // []
values([1, 2, 3]); // [1, 2, 3]
values(function(a, b) {return a + b;}); // []
values(new String('hello')); // ['h', 'e', 'l', 'l', 'o']
values(1); // throws exception
values(true); // throws exception
values(undefined); // throws exception
values(null); // throws exception

just-entries

npm install just-entries

yarn add just-entries

Return object entries as an array of [key, value] pairs

import entries from 'just-entries';

// Object:
entries({c: 8, a: 4}); // [['c', 8], ['a', 4]]
entries({b: {bb: 4}, a: {aa: 2}}); // [['b', {bb: 4}], ['a', {aa: 2}]]
entries({}); // []

// Array:
entries([{c: 8}, {a: 4}]); // [[0, {c: 8}], [1, {a: 4}]]
entries(['À', 'mauvais', 'ouvrier', 'point', 'de', 'bon', 'outil'])
// [[0, 'À'], [1, 'mauvais'] ... [6, 'outil']]
entries([]); // []

just-pick

npm install just-pick

yarn add just-pick

Copy an object but with only the specified keys

import pick from 'just-pick';

var obj = { a: 3, b: 5, c: 9 };
pick(obj, ['a', 'c']); // {a: 3, c: 9}
pick(obj, 'a', 'c'); // {a: 3, c: 9}
pick(obj, ['a', 'b', 'd']); // {a: 3, b: 5}
pick(obj, ['a', 'a']); // {a: 3}

just-omit

npm install just-omit

yarn add just-omit

Copy an object but omit the specified keys

import omit from 'just-omit';

var obj = {a: 3, b: 5, c: 9};
omit(obj, ['a', 'c']); // {b: 5}
omit(obj, 'a', 'c'); // {b: 5}
omit(obj, ['a', 'b', 'd']); // {c: 9}
omit(obj, ['a', 'a']); // {b: 5, c: 9}

just-is-empty

npm install just-is-empty

yarn add just-is-empty

Return true if object has no enumerable key values

import isEmpty from 'just-is-empty';
 isEmpty({a: 3, b: 5}) // false
 isEmpty([1, 2]) // false
 isEmpty(new Set([1, 2, 2])) // false
 isEmpty((new Map()).set('a', 2)) // false
 isEmpty({}) // true
 isEmpty([]) // true
 isEmpty(new Set()) // true
 isEmpty(new Map()) // true
 isEmpty('abc') // false
 isEmpty('') // true
 isEmpty(0) // true
 isEmpty(1) // true
 isEmpty(true) // true
 isEmpty(Symbol('abc')); // true
 isEmpty(//); // true
 isEmpty(new String('abc')); // false
 isEmpty(new String('')); // true
 isEmpty(new Boolean(true)); // true
 isEmpty(null) // true
 isEmpty(undefined) // true

just-is-circular

npm install just-is-circular

yarn add just-is-circular

Return true if object has a circular reference NOTE: not supported in IE or microsoft edge

import isCircular from 'just-is-circular';
const a = {};
a.b = a;
isCircular(a); // true

const a = {};
a.b = {
  c: a
};
isCircular(a); // true

const a = {};
a.b = {
  c: 4
};
isCircular(a); // false

const a = [];
a.push(a);
isCircular(a); // true

isCircular({}); // false
isCircular('hi'); // false
isCircular(undefined); // false

just-is-primitive

npm install just-is-primitive

yarn add just-is-primitive

Determine if a value is a primitive value

import isPrimitive from 'just-is-primitive';
isPrimitive('hi') // true
isPrimitive(3) // true
isPrimitive(true) // true
isPrimitive(false) // true
isPrimitive(null) // true
isPrimitive(undefined) // true
isPrimitive(Symbol()) // true
isPrimitive({}) // false
isPrimitive([]) // false
isPrimitive(function() {}) // false
isPrimitive(new Date()) // false
isPrimitive(/a/) // false

just-filter-object

npm install just-filter-object

yarn add just-filter-object

Filter an object

import filter from 'just-filter';

// returns a new object containing those original properties for which the predicate returns truthy
filter({a: 3, b: 5, c: 9}, (key, value) => value < 6); // {a: 3, b: 5}
filter({a1: 3, b1: 5, a2: 9}, (key, value) => key[0] == 'a'); // {a1: 3, a2: 9}
filter({a: 3, b: 5, c: null}, (key, value) => value); // {a: 3, b: 5}

just-map-object

npm install just-map-object

yarn add just-map-object

Map an object, passing key and value to predicates

import map from 'just-map-object';

// DEPRECATED: use just-map-values
map({a: 3, b: 5, c: 9}, (key, value) => value + 1); // {a: 4, b: 6, c: 10}
map({a: 3, b: 5, c: 9}, (key, value) => key); // {a: 'a', b: 'b', c: 'c'}
map({a: 3, b: 5, c: 9}, (key, value) => key + value); // {a: 'a3', b: 'b5', c: 'c9'}```

just-map-values

npm install just-map-values

yarn add just-map-values

Map an object, predicate updates values, receives (value, key, object)

import map from 'just-map-values';

// predicate updates values, receives (value, key, obj)
map({a: 3, b: 5, c: 9}, (value) => value + 1); // {a: 4, b: 6, c: 10}
map({a: 3, b: 5, c: 9}, (value, key) => value + key); // {a: 3a, b: 5b, c: 9c}
map({a: 3, b: 5, c: 9}, (value, key, obj) => obj.b); // {a: 5, b: 5, c: 5}

just-map-keys

npm install just-map-keys

yarn add just-map-keys

Map an object, predicate updates keys, receives (value, key, object)

import map from 'just-map-keys';

// predicate updates keys, receives (value, key, object)
map({a: 'cow', b: 'sheep', c: 'pig'}, (value) => value);
  // {cow: 'cow', sheep: 'sheep', pig: 'pig'}
map([4, 5, 6], (value, key) => key + 1); // {1: 4, 2: 5, 3: 6}
map({a: 3, b: 5, c: 9}, (value, key) => key + value); // {a3: 3, b5: 5, c9: 9}
map({a: 3, b: 5, c: 9}, (value, key, obj) => obj.b + value + key);
  // {'8a': 3, '10b': 5, '14c': 9}

just-deep-map-values

npm install just-deep-map-values

yarn add just-deep-map-values

Returns an object with values at all depths mapped according to the provided function

import deepMapValues from 'just-deep-map-values';

const squareFn = (number) => number * number;
deepMapValues({ a: 1, b: { c: 2, d: { e: 3 } } }, squareFn); // => { a: 1, b: { c: 4, d: { e: 9 } } }

just-reduce-object

npm install just-reduce-object

yarn add just-reduce-object

Reduce an object

import reduce from 'just-reduce-object';

// applies a function against an accumulator and each key-value pairs of the object
// to reduce it to a single value
reduce({a: 3, b: 5, c: 9}, (acc, key, value, index, keys) => {
  acc[value] = key;
  return acc;
}, {}); // {3: 'a', 5: 'b', 9: 'c'}

reduce({a: 3, b: 5, c: 9}, (acc, key, value, index, keys) => {
  acc += value;
  return acc;
}); // 17

just-safe-get

npm install just-safe-get

yarn add just-safe-get

Get value at property, don't throw if parent is undefined

import get from 'just-safe-get';

const obj = {a: {aa: {aaa: 2}}, b: 4};

get(obj, 'a.aa.aaa'); // 2
get(obj, ['a', 'aa', 'aaa']); // 2

get(obj, 'b.bb.bbb'); // undefined
get(obj, ['b', 'bb', 'bbb']); // undefined

get(obj.a, 'aa.aaa'); // 2
get(obj.a, ['aa', 'aaa']); // 2

get(obj.b, 'bb.bbb'); // undefined
get(obj.b, ['bb', 'bbb']); // undefined

get(obj.b, 'bb.bbb', 5); // 5
get(obj.b, ['bb', 'bbb'], true); // true

get(null, 'a'); // undefined
get(undefined, ['a']); // undefined

get(null, 'a', 42); // 42
get(undefined, ['a'], 42); // 42

const obj = {a: {}};
const sym = Symbol();
obj.a[sym] = 4;
get(obj.a, sym); // 4

just-safe-set

npm install just-safe-set

yarn add just-safe-set

Set value at property, create intermediate properties if necessary

import set from 'just-safe-set';

const obj1 = {};
set(obj1, 'a.aa.aaa', 4); // true
obj1; // {a: {aa: {aaa: 4}}}

const obj2 = {};
set(obj2, ['a', 'aa', 'aaa'], 4); // true
obj2; // {a: {aa: {aaa: 4}}}

const obj3 = {a: {aa: {aaa: 2}}};
set(obj3, 'a.aa.aaa', 3); // true
obj3; // {a: {aa: {aaa: 3}}}

const obj5 = {a: {}};
const sym = Symbol();
set(obj5.a, sym, 7); // true
obj5; // {a: {Symbol(): 7}}

just-typeof

npm install just-typeof

yarn add just-typeof

Type inferer

import typeOf from 'just-typeof';

typeOf({}); // 'object'
typeOf([]); // 'array'
typeOf(function() {}); // 'function'
typeOf(/a/); // 'regexp'
typeOf(new Date()); // 'date'
typeOf(null); // 'null'
typeOf(undefined); // 'undefined'
typeOf('a'); // 'string'
typeOf(1); // 'number'
typeOf(true); // 'boolean'

just-flip-object

npm install just-flip-object

yarn add just-flip-object

Flip the keys and values

import flip from 'just-flip-object';

// flip the key and value
flip({a: 'x', b: 'y', c: 'z'}); // {x: 'a', y: 'b', z: 'c'}
flip({a: 1, b: 2, c: 3}); // {'1': 'a', '2': 'b', '3': 'c'}
flip({a: false, b: true}); // {false: 'a', true: 'b'}

just-has

npm install just-has

yarn add just-has

Return a boolen indicating the existence of a deep property, don't throw if parent is undefined

import has from 'just-has';

const obj = {a: {aa: {aaa: 2}}, b: 4};

has(obj, 'a.aa.aaa'); // true
has(obj, ['a', 'aa', 'aaa']); // true

has(obj, 'b.bb.bbb'); // false
has(obj, ['b', 'bb', 'bbb']); // false

has(obj.a, 'aa.aaa'); // true
has(obj.a, ['aa', 'aaa']); // true

has(obj.b, 'bb.bbb'); // false
has(obj.b, ['bb', 'bbb']); // false

has(null, 'a'); // false
has(undefined, ['a']); // false

const obj = {a: {}};
const sym = Symbol();
obj.a[sym] = 4;
has(obj.a, sym); // true

Arrays

just-cartesian-product

npm install just-cartesian-product

yarn add just-cartesian-product

Takes an input of an array of arrays and returns their Cartesian product.

import cartesianProduct from 'just-cartesian-product';

cartesianProduct([[1, 2], ['a', 'b']]); // [[1, 'a'], [1, 'b'], [2, 'a'], [2, 'b']]
cartesianProduct([[1, 2], ['a', 'b', 'c']]); // [[1, 'a'], [1, 'b'], [1, 'c'], [2, 'a'], [2, 'b'], [2, 'c']]
cartesianProduct([]); // []
cartesianProduct(); // throws

just-unique

npm install just-unique

yarn add just-unique

Dedupes an array

import unique from 'just-unique';

unique([1, 2, 3, 2, 3, 4, 3, 2, 1, 3]); // [1, 2, 3, 4]

var a = {a: 3};
var b = {b: 4};
var c = {c: 5};
unique([a, a, b, c, b]); // [a, b, c]

unique([1, '1', 2, '2', 3, 2]); // [1, '1', 2, '2', 3]

// declaring sorted array for performance
unique([1, 1, '1', 2, 2, 5, '5', '5'], true); // [1, '1', 2, 5, '6']

// declaring strings array for performance
unique(['a', 'c', 'b', 'c', 'a'], false, true); // ['a', 'b', 'c']

just-flatten-it

npm install just-flatten-it

yarn add just-flatten-it

Return a flattened array

import flatten from 'just-flatten-it';

flatten([[1, [2, 3]], [[4, 5], 6, 7, [8, 9]]]);
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

flatten([[1, [2, 3]], [[4, 5], 6, 7, [8, 9]]], 1);
// [1, [2, 3], [[4, 5], 6, 7, [8, 9]]]

just-index

npm install just-index

yarn add just-index

Return an object from an array, keyed by the value at the given id

import index from 'just-index';

index([{id: 'first', val: 1}, {id: 'second', val: 2}], 'id');
// {first: {id: 'first', val: 1}, second: {id: 'second', val: 2}}
index([{id: 'first', val: 1}, null], 'id'); // {first: {id: 'first', val: 1}}
index([], 'id'); // {}
index([], null); // undefined
index({}, 'id'); // undefined

just-insert

npm install just-insert

yarn add just-insert

Inserts a sub-array into an array starting at the given index. Returns a copy

import insert from 'just-insert';

insert([1, 2, 5, 6], ['a', 'c', 'e'], 2); // [1, 2, 'a', 'c', 'e', 5, 6]
insert([1, 2, 5, 6], 'a', 2); // [1, 2, 'a', 5, 6]
insert([1, 2, 5, 6], ['a', 'c', 'e'], 0); // ['a', 'c', 'e', 1, 2, 5, 6]
insert([1, 2, 5, 6], ['a', 'c', 'e']); // ['a', 'c', 'e', 1, 2, 5, 6]

just-intersect

npm install just-intersect

yarn add just-intersect

Return the intersect of two arrays

import intersect from 'just-intersect';

intersect([1, 2, 5, 6], [2, 3, 5, 6]); // [2, 5, 6]
intersect([1, 2, 2, 4, 5], [3, 2, 2, 5, 7]); // [2, 5]

just-compact

npm install just-compact

yarn add just-compact

Returns a copy of an array with falsey values removed

import compact from 'just-compact';

compact([1, null, 2, undefined, null, NaN, 3, 4, false, 5]); // [1, 2, 3, 4, 5]
compact([1, 2, [], 4, {}]); // [1, 2, [], 4, {}]
compact([]); // []
compact({}); // throws

just-last

npm install just-last

yarn add just-last

Return the last member of an array

import last from 'just-last';

last([1, 2, 3, 4, 5]); // 5
last([{a: 1}, {b: 1}, {c: 1}]); // {c: 1}
last([true, false, [true, false]]); // [true, false]
last(); // undefined
last([]); // undefined
last(null); // undefined
last(undefined); // undefined

just-tail

npm install just-tail

yarn add just-tail

Return all but the first element of an array

import tail from 'just-tail';

tail([1, 2, 3, 4, 5]); // [2, 3, 4, 5]
tail([{a: 1}, {b: 1}, {c: 1}]); // [{b: 1}, {c: 1}]
tail([true, false, [true, false]]); // [false, [true, false]]
tail([]); // []
tail(); // undefined
tail(null); // undefined
tail(undefined); // undefined

just-random

npm install just-random

yarn add just-random

Return a randomly selected element in an array

import random from 'just-random';

random([1, 2, 3]);
// one of [1, 2, 3], at random

just-shuffle

npm install just-shuffle

yarn add just-shuffle

Return the elements of an array in random order

import shuffle from 'just-shuffle';

shuffle([1, 2, 3]); 
// array with original elements randomly sorted
shuffle([1, 2, 3], {shuffleAll: true}); 
// array with original elements randomly sorted and all in new postions
shuffle([]); // []
shuffle([1]); // [1]
shuffle(); // throws
shuffle(undefined); // throws
shuffle(null); // throws
shuffle({}); // throws

just-split

npm install just-split

yarn add just-split

Splits array into groups of n items each

import split from 'just-split';

split([]); // []
split([1, 2, 3, 4, 5]); // [[1, 2, 3, 4, 5]]
split([1, 2, 3, 4, 5, 6, 7, 8, 9], 3); // [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
split([1, 2, 3, 4, 5, 6, 7, 8, 9], '3'); // [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
split(['a', 'b', 'c', 'd', 'e'], 2); // [['a', 'b'], ['c', 'd'], ['e']]
split([1, 2, 3, 4, 5, 6, 7, 8], 3); // [[1, 2, 3], [4, 5, 6], [7, 8]]

just-split-at

npm install just-split-at

yarn add just-split-at

Splits an array into two at a given position

import splitAt from 'just-split-at';

splitAt([1, 2, 3, 4, 5], 2); // [[1, 2], [3, 4, 5]]
splitAt([{a: 1}, {b: 1}, {c: 1}], -1); // [[{a: 1}, {b: 1}], [{c: 1}]]
splitAt([], 2); // [[], []]
splitAt(null, 1); // throws
splitAt(undefined, 1); // throws

just-order-by

npm install just-order-by

yarn add just-order-by

Produces a new array, sorted in given order

import orderBy from 'just-order-by';

orderBy([10, 1, 5, 20, 15, 35, 30, 6, 8]); // [1, 5, 6, 8, 10, 15, 20, 30, 35]

orderBy(
  [
    { user: 'fabio', details: { city: 'Milan', age: 34 } },
    { user: 'max', details: { city: 'Munich', age: 29 } },
    { user: 'zacarias', details: { city: 'Sao Paulo', age: 44 } },
    { user: 'robert', details: { city: 'Manchester', age: 28 } },
    { user: 'max', details: { city: 'Zurich', age: 38 } },
  ],
  [
    {
      property(v) {
        return v.details.age;
      },
    },
  ]
);

/*
[
  {user: 'robert', age: 28},
  {user: 'max', age: 29},
  {user: 'fabio', age: 34},
  {user: 'klaus', age: 38},
  {user: 'zacarias', age: 44},
]
*/

orderBy(
  [
    {user: 'fabio', age: 34},
    {user: 'max', age: 29},
    {user: 'zacarias', age: 44},
    {user: 'robert', age: 28},
    {user: 'klaus', age: 38},
  ],
  [
    {
      property: 'user',
    },
  ]
);

/*
[
  {user: 'fabio', age: 34},
  {user: 'klaus', age: 38},
  {user: 'max', age: 29},
  {user: 'robert', age: 28},
  {user: 'zacarias', age: 44},
]
*/

orderBy(
  [
    { user: 'fabio', age: 34 },
    { user: 'max', age: 29 },
    { user: 'zacarias', age: 44 },
    { user: 'moris', age: 28 },
    { user: 'max', age: 38 },
  ],
  [
    {
      property: 'user',
      order: 'desc',
    },
    {
      property(v) {
        return v.age;
      },
    },
  ]
);

/*
[
  {
    user: 'zacarias',
    age: 44
  },
  {
    user: 'moris',
    age: 28
  },
  {
    user: 'max',
    age: 29
  },
  {
    user: 'max',
    age: 38
  },
  {
    user: 'fabio',
    age: 34
  }
]
*/

just-sort-by

npm install just-sort-by

yarn add just-sort-by

Produces a new array, sorted in ascending order

import sortBy from 'just-sort-by';

sortBy([10, 1, 5, 20, 15, 35, 30, 6, 8]); // [1, 5, 6, 8, 10, 15, 20, 30, 35]

sortBy([
  {user: 'fabio', details: {city: "Milan", age: 34}},
  {user: 'max', details: {city: "Munich", age: 29}},
  {user: 'zacarias', details: {city: "Sao Paulo", age: 44}},
  {user: 'robert', details: {city: "Manchester", age: 28}},
  {user: 'klaus', details: {city: "Zurich", age: 38}},
], function(o) {
  return o.details.age;
});

/*
[
  {user: 'robert', age: 28},
  {user: 'max', age: 29},
  {user: 'fabio', age: 34},
  {user: 'klaus', age: 38},
  {user: 'zacarias', age: 44},
]
*/

sortBy([
  {user: 'fabio', age: 34},
  {user: 'max', age: 29},
  {user: 'zacarias', age: 44},
  {user: 'robert', age: 28},
  {user: 'klaus', age: 38},
], 'user');
/*
[
  {user: 'fabio', age: 34},
  {user: 'klaus', age: 38},
  {user: 'max', age: 29},
  {user: 'robert', age: 28},
  {user: 'zacarias', age: 44},
]
*/

just-partition

npm install just-partition

yarn add just-partition

Elements satisfying predicate added to first array, remainder added to second

import partition from 'just-partition';

partition([1, 5, 2, 4, 3], n => n > 3); // [[5, 4],[1, 2, 3]]
partition(['a', 2, 3, '3'], x => typeof x == 'string'); // [['a', '3'],[2, 3]]
partition([1, 2, 3, 4], x => typeof x == 'number'); // [[1, 2, 3, 4],[]]
partition([1, 2, 3, 4], x => typeof x == 'string'); // [[], [1, 2, 3, 4]]
partition([], n => n > 3); // [[], []]
partition({a: 1, b: 2}, n => n > 1); // throws
partition(null, n => n > 1); // throws
partition(undefined, n => n > 1); // throws

just-permutations

npm install just-permutations

yarn add just-permutations

Returns all permutations of the length N of the elements of the given Array

import permutations from 'just-permutations';

permutations([1, 2, 3]); // [[1, 2, 3], [2, 1, 3], [2, 3, 1], [1, 3, 2], [3, 1, 2], [3, 2, 1]]
permutations([]); // []
permutations(); // throws

just-range

npm install just-range

yarn add just-range

Generate a range array for numbers

import range from 'just-range';

range(1, 5); // [1, 2, 3, 4]
range(5); // [0, 1, 2, 3, 4]
range(-5); // [0, -1, -2, -3, -4]
range(0, 20, 5) // [0, 5, 10, 15]

just-remove

npm install just-remove

yarn add just-remove

Removes one array from another

import remove from 'just-remove';

remove([1, 2, 3, 4, 5, 6], [1, 3, 6]); // [2, 4, 5]

just-union

npm install just-union

yarn add just-union

Returns the union of two arrays

import union from 'just-union';

union([1, 2, 5, 6], [2, 3, 4, 6]); // [1, 2, 5, 6, 3, 4]

just-zip-it

npm install just-zip-it

yarn add just-zip-it

Returns an array of grouped elements, taking n-th element from every given array

import zip from 'just-zip-it';

zip([1, 2, 3]); // [[1], [2], [3]]
zip([1, 2, 3], ['a', 'b', 'c']); // [[1, 'a'], [2, 'b'], [3, 'c']]
zip([1, 2], ['a', 'b'], [true, false]); //[[1, 'a', true], [2, 'b', false]]

zip(undefined, {}, false, 1, 'foo'); // []
zip([1, 2], ['a', 'b'], undefined, {}, false, 1, 'foo'); // [[1, 'a'], [2, 'b']]

zip([1, 2, 3], ['a', 'b'], [true]); // [[1, 'a', true], [2, 'b', undefined], [3, undefined, undefined]]

just-group-by

npm install just-group-by

yarn add just-group-by

Return a grouped object from array

import groupBy from 'just-group-by';

groupBy([6.1, 4.2, 6.3], Math.floor); // { '4': [4.2], '6': [6.1, 6.3] }
groupBy([1,2,3,4,5,6,7,8], function(i) { return i % 2}); // { '0': [2, 4, 6, 8], '1': [1, 3, 5, 7] }

Statistics

just-mean

npm install just-mean

yarn add just-mean

The mean (average) value in an array

import mean from 'just-mean';

mean([1, 2, 3, 2, 4, 1]); // 2.1666666667
mean(3, 2, 1); // 2
mean([4]); // 4
mean(['3', 2]); // throws
mean(); // throws

just-median

npm install just-median

yarn add just-median

Return the median value of an array of numbers

import median from 'just-median';

median([1, 2, 3, 4, 5]); // 3
median([3, -1, 2]); // 2
median([9, 14, 14, 200, 15]); // 14
median(1, 2, 4, 3); // 2.5
median(['3', 2, 1]); // throws
median(); // throws

just-mode

npm install just-mode

yarn add just-mode

Return the most frequently occuring number(s)

import mode from 'just-mode';

mode([1, 2, 3, 2]); // 2
mode(4, 4, 1, 4); // 4
mode(100, 100, 101, 101); // [100, 101]
mode(4, 3, 2, 1); // [1, 2, 3, 4]
mode(['1', 2, 2, 1, 2]); // throws
mode(null); // throws

just-percentile

npm install just-percentile

yarn add just-percentile

Return the value at the given percentile (using linear interpolation)

import percentile from 'just-percentile';

percentile([1, 2, 3], 0); // 1
percentile([1, 2, 3], 0.5); // 2
percentile([1, 2, 3], 1); // 3

// See https://en.wikipedia.org/wiki/Percentile (linear interpolation method)
percentile([15, 20, 35, 40, 50], 0.05); // 15
percentile([15, 20, 35, 40, 50], 0.3); // 20
percentile([15, 20, 35, 40, 50], 0.4); // 27.5
percentile([15, 20, 35, 40, 50], 0.95); // 50

percentile(1, 2, 3, 50); // throws
percentile(['1', 2, 3], 50); // throws
percentile([], 50); // throws

just-variance

npm install just-variance

yarn add just-variance

Return the standard deviation of an array or numeric argument list

import variance from 'just-variance';

variance([1, 2, 3, 2, 4, 1]); // 1.3666666667
variance(3, 2, 1); // 1
variance([100, 100, 100.1, 100]); // 0.0025
variance(1, 2, 3, 4, 5, -6); // 15.5
variance([4]); // throws
variance(['3', 2]); // throws
variance(NaN, NaN); // throws
variance(); // throws

just-standard-deviation

npm install just-standard-deviation

yarn add just-standard-deviation

Return the standard deviation of an array or numeric argument list

import standardDeviation from "just-standard-deviation";

standardDeviation([1, 2, 3, 2, 4, 1]); // 1.16904519
standardDeviation(3, 2, 1); // 1
standardDeviation([100, 100, 100.1, 100]); // 0.05
standardDeviation(1, 2, 3, 4, 5, -6); // 3.9370039
standardDeviation([4]); // throws
standardDeviation(["3", 2]); // throws
standardDeviation(NaN, NaN); // throws
standardDeviation(); // throws

just-skewness

npm install just-skewness

yarn add just-skewness

Return the skewness of an array or numeric argument list using Pearson's second skewness coefficient

import skewness from "just-skewness";

// Using Pearson's second skewness coefficient
skewness(3, 2, 1); // 0
skewness([1, 2, 3, 2, 4, 1]); // 0.4276994613841504
skewness(1, 2, 3, 4, 5, -6); // -0.762000762001143
skewness([1, 2, 3, 4, 9]); // 0.7705935588815224
skewness([4]); // throws
skewness(["3", 2]); // throws
skewness(NaN, NaN); // throws
skewness(); // throws

Strings

just-template

npm install just-template

yarn add just-template

Interpolate a string with variables

import template from 'just-template';

var data = {
  a: {
    aa: {
      aaa: 'apple',
      bbb: 'pear'
    },
    bb: 'orange'
  },
  b: 'plum'
};
template('2 {{a.aa.aaa}}s, a {{a.aa.bbb}}, 3 {{a.bb}}s and a {{b}}. Yes 1 {{a.aa.bbb}}.', data);
// '2 apples, a pear, 3 oranges and a plum. Yes 1 pear.'

just-truncate

npm install just-truncate

yarn add just-truncate

Truncate a string with a custom suffix

  truncate('when shall we three meet again', 9); // 'when s...'
  truncate('when shall we three meet again', 10, ' (etc)'); // 'when (etc)'
  truncate('when shall we', 15,); // 'when shall we'
  truncate('when shall we', 15, '(more)'); // 'when shall we'
  truncate('when shall we', 10, ' (etc etc etc)'); // ' (etc etc etc)'

just-prune

npm install just-prune

yarn add just-prune

Prune a string with whole words and a custom suffix

  prune('when shall we three meet again', 7); // 'when...'
  prune('when shall we three meet again', 7, ' (more)'; // 'when (more)'
  prune('when shall we', 15,); // 'when shall we'
  prune('when shall we', 15, ' (etc)'); // 'when shall we'
  prune('when shall we', 7, ' (more)'); // ' (more)'

just-squash

npm install just-squash

yarn add just-squash

Remove all spaces from a string, optionally remove escape sequences too

  squash('the cat sat on the mat'); // 'thecatsatonthemat'
  squash(' the cat sat on the mat '); // 'thecatsatonthemat'
  squash('\tthe cat\n sat \fon \vthe \rmat '); // '\tthecat\nsat\fon\vthe\rmat'
  squash('\tthe cat\n sat \fon \vthe \rmat ', true); // 'thecatsatonthemat'
  squash(`the cat
sat on the mat`, true); // thecatsatonthemat

just-left-pad

npm install just-left-pad

yarn add just-left-pad

Add characters to the left of a string such that its total length is n

import leftPad from 'just-left-pad';

leftPad('hello', 9); // '    hello'
leftPad('hello', 3); // 'hello'
leftPad('hello', 9, '.'); // '....hello'
leftPad('hello', 9, '..'); // '....hello'
leftPad('hello', 10, 'ab'); // 'bababhello'
leftPad('hello', 9, '\uD83D\uDC04'); // '🐄🐄🐄🐄hello'
leftPad('hello', 10, '\uD83D\uDC11\uD83D\uDC04'), // '🐄🐑🐄🐑🐄hello'
leftPad('hello', 7, '🐄'), // '🐄🐄hello'
leftPad(null, 7); // throws
leftPad([], 4, '*'); // throws
leftPad('hello', 4, true); // throws
leftPad('hello', -4, true); // throws  
leftPad('hello', 2.3, true); // throws

just-right-pad

npm install just-right-pad

yarn add just-right-pad

Add characters to the right of a string such that its total length is n

import rightPad from 'just-right-pad';

rightPad('hello', 9); // 'hello    '
rightPad('hello', 3); // 'hello'
rightPad('hello', 9, '.'); // 'hello....'
rightPad('hello', 9, '..'); // 'hello....'
rightPad('hello', 10, 'ab'); // 'helloababa'
rightPad('hello', 9, '\uD83D\uDC04'); // 'hello🐄🐄🐄🐄'
rightPad('hello', 10, '\uD83D\uDC11\uD83D\uDC04'), // 'hello🐑🐄🐑🐄🐑'
rightPad('hello', 7, '🐄'), // 'hello🐄🐄'
rightPad(null, 7); // throws
rightPad([], 4, '*'); // throws
rightPad('hello', 4, true); // throws
rightPad('hello', -4, true); // throws  
rightPad('hello', 2.3, true); // throws

just-camel-case

npm install just-camel-case

yarn add just-camel-case

Convert a string to camel case

  import camelCase from 'just-camel-case';

  camelCase('the quick brown fox'); // 'theQuickBrownFox'
  camelCase('the_quick_brown_fox'); // 'theQuickBrownFox'
  camelCase('the-quick-brown-fox'); // 'theQuickBrownFox'
  camelCase('theQuickBrownFox'); // 'theQuickBrownFox'
  camelCase('thequickbrownfox'); // 'thequickbrownfox'
  camelCase('the - quick * brown# fox'); // 'theQuickBrownFox'
  camelCase('behold theQuickBrownFox'); // 'beholdTheQuickBrownFox'
  camelCase('Behold theQuickBrownFox'); // 'beholdTheQuickBrownFox'
  // all caps words are camel-cased
  camelCase('The quick brown FOX'), 'theQuickBrownFox');
  // all caps substrings >= 4 chars are camel-cased
  camelCase('theQUickBrownFox'); // 'theQUickBrownFox'
  camelCase('theQUIckBrownFox'); // 'theQUIckBrownFox'
  camelCase('theQUICKBrownFox'); // 'theQuickBrownFox'

just-kebab-case

npm install just-kebab-case

yarn add just-kebab-case

Convert a string to kebab case

  import kebabCase from 'just-kebab-case';

  kebabCase('the quick brown fox'); // 'the-quick-brown-fox'
  kebabCase('the-quick-brown-fox'); // 'the-quick-brown-fox'
  kebabCase('the_quick_brown_fox'); // 'the-quick-brown-fox'
  kebabCase('theQuickBrownFox'); // 'the-quick-brown-fox'
  kebabCase('theQuickBrown Fox'); // 'the-quick-brown-fox'
  kebabCase('thequickbrownfox'); // 'thequickbrownfox'
  kebabCase('the - quick * brown# fox'); // 'the-quick-brown-fox'
  kebabCase('theQUICKBrownFox'); // 'the-q-u-i-c-k-brown-fox'

just-snake-case

npm install just-snake-case

yarn add just-snake-case

Convert a string to snake case

  import snakeCase from 'just-snake-case';

  snakeCase('the quick brown fox'); // 'the_quick_brown_fox'
  snakeCase('the-quick-brown-fox'); // 'the_quick_brown_fox'
  snakeCase('the_quick_brown_fox'); // 'the_quick_brown_fox'
  snakeCase('theQuickBrownFox'); // 'the_quick_brown_fox'
  snakeCase('thequickbrownfox'); // 'thequickbrownfox'
  snakeCase('the - quick * brown# fox'); // 'the_quick_brown_fox'
  snakeCase('theQUICKBrownFox'); // 'the_q_u_i_c_k_brown_fox'

just-pascal-case

npm install just-pascal-case

yarn add just-pascal-case

Convert a string to pascal case

  import pascalCase from 'just-pascal-case';

  pascalCase('the quick brown fox'); // 'TheQuickBrownFox'
  pascalCase('the_quick_brown_fox'); // 'TheQuickBrownFox'
  pascalCase('the-quick-brown-fox'); // 'TheQuickBrownFox'
  pascalCase('theQuickBrownFox'); // 'TheQuickBrownFox'
  pascalCase('thequickbrownfox'); // 'Thequickbrownfox'
  pascalCase('the - quick * brown# fox'); // 'TheQuickBrownFox'
  pascalCase('theQUICKBrownFox'); // 'TheQUICKBrownFox'

just-capitalize

npm install just-capitalize

yarn add just-capitalize

Capitalize the first character of a string

  import capitalize from 'just-capitalize';

/*
  capitalize('capitals'); // 'Capitals'
  capitalize('Capitals'); // 'Capitals'
  capitalize('many words'); // 'Many words'
  capitalize('!exclaim'); // '!exclaim'
*/

just-replace-all

npm install just-replace-all

yarn add just-replace-all

Replace all occurrences of a string within a string with another string

  import replaceAll from 'just-replace-all';

/*
  replaceAll('hello, world', 'l', 'q'); // 'heqqo, worqd'
  replaceAll('hello, world', 'l', 'qq'); // 'heqqqqo, worqqd'
  replaceAll('hello, world', 'll', 'q'); // 'heqo, world'
  replaceAll('hello, world', '', 'q'); // 'hello, world'
  replaceAll('hello, world', 'l', ''); // 'heo, word'
  replaceAll('hello, world', null, 'q'); // 'hello, world'
  replaceAll('hello, world', 'l'); // throw
  replaceAll('hello, world'); // throw
  replaceAll(); // throw
  replaceAll(null, 'l', 'q'); // throw
  replaceAll('hello, world', null, 'q'); // throw
  replaceAll('hello, world', 'l', null); // throw
*/

Numbers

just-clamp

npm install just-clamp

yarn add just-clamp

Restrict a number within a range

import clamp from 'just-clamp';

var n = 5;
clamp(1, n, 12); // 5
clamp(3, n, 1); // 3
clamp(8, n, 9); // 8
clamp(0, n, 0); // 0

var n = -5;
clamp(1, n, 12); // 1
clamp(-7, n, -8); // -7

clamp(NaN, n, 8); // NaN
clamp(3, n, NaN); // NaN  
clamp(3, NaN, 8); // NaN    

clamp(undefined, n, 8); // throws
clamp(3, n, 'h'); // throws  
clamp(3, false, 8); // throws

just-is-prime

npm install just-is-prime

yarn add just-is-prime

Check if number is prime

  import isPrime from 'just-is-prime;

/*
  isPrime(1); // false
  isPrime(2); // true
  isPrime(17); // true
  isPrime(10); // false
  isPrime(); // throws
  isPrime(null); // throws
  isPrime("js"); // throws
  isPrime({}); // throws
  isPrime(function() {}); // throws
  isPrime([]); // throws
*/

just-modulo

npm install just-modulo

yarn add just-modulo

Modulo of a number and a divisor

import modulo from 'just-modulo';

modulo(7, 5); // 2
modulo(17, 23); // 17
modulo(16.2, 3.8); // 1
modulo(5.8, 3.4); //2.4
modulo(4, 0); // 4
modulo(-7, 5); // 3
modulo(-2, 15); // 13
modulo(-5.8, 3.4); // 1
modulo(12, -1); // NaN
modulo(-3, -8); // NaN
modulo(12, 'apple'); // NaN
modulo('bee', 9); // NaN
modulo(null, undefined); // NaN

just-random-integer

npm install just-random-integer

yarn add just-random-integer

Produces a random integer within a given range

import random from 'just-random-integer';

random();
// Returns either 0 or 1
random(5);
// Returns a random integer between 0 and 5 (inclusively)
random(3, 10);
// Returns a random integer between 3 and 10 (inclusively)
random(-5.8, 10.4);
// Returns a random integer between -5 and 10 (inclusively)

Functions

just-compose

npm install just-compose

yarn add just-compose

Return a function composed of 2 or more functions

import compose from 'just-compose';

const sqRootBiggest = compose(Math.max, Math.sqrt, Math.trunc);
sqRootBiggest(10, 5); // 3
sqRootBiggest(7, 0, 16); // 4

just-curry-it

npm install just-curry-it

yarn add just-curry-it

Return a curried function

import curry from 'just-curry-it';

function add(a, b, c) {
  return a + b + c;
}
curry(add)(1)(2)(3); // 6
curry(add)(1)(2)(2); // 5
curry(add)(2)(4, 3); // 9

function add(...args) {
  return args.reduce((sum, n) => sum + n, 0)
}
var curryAdd4 = curry(add, 4)
curryAdd4(1)(2, 3)(4); // 10

function converter(ratio, input) {
  return (input*ratio).toFixed(1);
}
const curriedConverter = curry(converter)
const milesToKm = curriedConverter(1.62);
milesToKm(35); // 56.7
milesToKm(10); // 16.2

just-demethodize

npm install just-demethodize

yarn add just-demethodize

Turn a method into a standalone function; the first arg becomes this

import demethodize from 'just-demethodize';

const trimFn = demethodize(''.trim);
['hello ', ' goodbye', 'hello again'].map(trimFn); // ['hello', 'goodbye', 'hello again']

just-flip

npm install just-flip

yarn add just-flip

Flip first two arguments of a function

import flip from 'just-flip';

flip(console.log)(1, 2, 3) // 2, 1, 3

import map from 'just-map-object';
import partial from 'just-partial';

const numbers = {x: 5, y: 10};
const flippedMap = flip(map);
const double = partial(flippedMap, (undefined, number) => number * 2);
double(numbers) // {x: 10, y: 20];

just-partial-it

npm install just-partial-it

yarn add just-partial-it

Return a partial function

import partial from 'just-partial-it';

const cubedRoot = partial(Math.pow, _, 1/3);
cubedRoot(64); // 4

const getRoot = partial(Math.pow, 64);
getRoot(1/2); // 8

just-pipe

npm install just-pipe

yarn add just-pipe

Pass a value through a pipeline of functions

import pipe from 'just-pipe

pipe(3, a => a+1, b => b*2) // 8
pipe('John Smith', a => a.split(' '), b => b.reverse(), c => c[0]) // 'Smith'

just-debounce-it

npm install just-debounce-it

yarn add just-debounce-it

Return a debounced function

import debounce from "just-debounce-it";

const fn1 = debounce(() => console.log("Hello"), 500);
fn1();
fn1();
fn1();
// 500ms later logs 'hello' once

const fn2 = debounce(() => console.log("Hello"), 500, true);
fn2(); // logs hello immediately
fn2();
fn2();
// 500ms later logs 'hello' once

const fn3 = debounce(() => console.log("Hello"), 500);
fn3();
fn3();
fn3();
fn3.cancel();
// function cancelled before 'hello' is logged

const fn4 = debounce(() => console.log("Hello"), 500);
fn4();
fn4();
fn4();
fn4.flush();
// immediately invoke the debounced function

just-memoize

npm install just-memoize

yarn add just-memoize

An implementation of the memoize technique

import memoize from 'just-memoize';

const sumByOne = memoize(function(value) {
  return value + 1;
});

sumByOne(10); // Returns value returned by the function
sumByOne(10); // Cache hit!

sumByOne(20); // Returns value returned by the function
sumByOne(20); // Cache hit!

// Custom cache key (key defaults to JSON stringified arguments)
var sum = memoize(function(a, b) {
  return a + b;
}, function(a, b) {
  return `${a}-${b}`;
});

sum(10, 10); // Returns value returned by the function
sum(10, 20); // Returns value returned by the function
sum(10, 20); // Cache hit!

just-memoize-last

npm install just-memoize-last

yarn add just-memoize-last

A memoize implementation that only caches the most recent evaluation

const memoizeLast = require('just-memoize-last')
const compare = require('just-compare')

const maxValue = memoizeLast(function(arr) {
  return Math.max(...arr)
}, function(a, b) {
  return compare(a, b)
});

maxValue([1,2,3]) // 3
maxValue([1,2,3]) // cache hit!
maxValue([1,3,4]) // 4
maxValue([1,2,3]) // 3

just-random

npm install just-random

yarn add just-random

Return a randomly selected element in an array

import random from 'just-random';

random([1, 2, 3]);
// one of [1, 2, 3], at random

just-throttle

npm install just-throttle

yarn add just-throttle

Return a throttled function

import throttle from 'just-throttle';

// no matter how many times the function is called, only invoke once within the given interval
// options: 
// `leading`: invoke  before interval
// `trailing`: invoke afer interval

const fn1 = throttle(() => console.log('hello'), 500, {leading: true});
setInterval(fn1, 400);
// logs 'hello' immediately and then every 500ms

const fn2 = throttle(() => console.log('hello'), 500, {trailing: true});
setInterval(fn2, 400);
// logs 'hello' after 500ms and then every 500ms

const fn3 = throttle(() => console.log('hello'), 500, {leading: true, trailing: true});
// forces trailing to false

const fn4 = throttle(() => console.log('hello'), 500, { leading: false });
fn4();
fn4();
fn4();
fn4.cancel();
// function cancelled before 'hello' is logged

const fn5 = throttle(() => console.log("Hello"), 500);
fn5();
fn5();
fn5();
fn5.flush();
// immediately invoke the throttled function

just-once

npm install just-once

yarn add just-once

Create a function that can only be invoked once

import once from 'just-once';

const fn = once(() => console.log('hello'));

fn();
// logs 'hello'
fn();
// does nothing

Testing

Run all tests as a single test suite with

npm run test

Cross browser tests (via saucelabs) are in the sauce branch

Contribute!

https://github.com/angus-c/just/blob/master/CONTRIBUTING.md