feat(paths): add exists() path checker & tests

thi-ng · Sep 1, 2018 · f018353 · f018353
1 parent e66a492
commit f018353
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Showing 2 changed files with 45 additions and 1 deletion.
diff --git a/packages/paths/src/index.ts b/packages/paths/src/index.ts
@@ -32,6 +32,33 @@ export function toPath(path: Path) {
     return isArray(path) ? path : isString(path) ? path.length > 0 ? path.split(".") : [] : path != null ? [path] : [];
 }
 
+/**
+ * Takes an arbitrary object and lookup path. Descends into object along
+ * path and returns true if the full path exists (even if final leaf
+ * value is `null` or `undefined`). Checks are performed using
+ * `hasOwnProperty()`.
+ *
+ * @param obj
+ * @param path
+ */
+export const exists = (obj: any, path: Path) => {
+    if (obj == null) {
+        return false;
+    }
+    path = toPath(path);
+    for (let n = path.length - 1, i = 0; i <= n; i++) {
+        const k = path[i];
+        if (!obj.hasOwnProperty(k)) {
+            return false;
+        }
+        obj = obj[k];
+        if (obj == null && i < n) {
+            return false;
+        }
+    }
+    return true;
+};
+
 /**
  * Composes a getter function for given nested lookup path. Optimized
  * fast execution paths are provided for path lengths less than 5.

diff --git a/packages/paths/test/index.ts b/packages/paths/test/index.ts
@@ -1,5 +1,5 @@
 import * as assert from "assert";
-import { setIn } from "../src/index";
+import { exists, setIn } from "../src/index";
 
 describe("paths", () => {
     it("setIn (len = 0)", () => {
@@ -150,4 +150,21 @@ describe("paths", () => {
         assert(a.x.y === b.x.y);
         assert(a.u === b.u);
     });
+
+    it("exists", () => {
+        const a = { a: { b: null } };
+        const b = { x: { y: { z: [1, 2, { u: 3, v: undefined }] } } };
+        assert(!exists(null, "x.y.z"), "x.y.z");
+        assert(!exists(0, "x.y.z"), "x.y.z");
+        assert(exists("", "length"), "length");
+        assert(exists(a, "a.b"), "a.b");
+        assert(!exists(a, "a.b.c"), "a.b.c");
+        assert(exists(b, "x"), "x");
+        assert(exists(b, "x.y.z"), "x.y.z");
+        assert(exists(b, "x.y.z.2.u"), "x.y.z.2.u");
+        assert(exists(b, "x.y.z.2.v"), "x.y.z.2.v");
+        assert(!exists(b, "x.y.z.3"), "x.y.z.3");
+        assert(!exists(b, "x.y.z.3.u"), "x.y.z.3.u");
+        assert(!exists(b, "x.z.y.2.u"), "x.z.y.2.u");
+    })
 });