Initial implementation.

inspect-js · Sep 19, 2016 · 33f5cc6 · dartdl · May 7, 2020 · ljharb
1 parent 88a337c
commit 33f5cc6
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diff --git a/index.js b/index.js
@@ -0,0 +1,13 @@
+'use strict';
+
+var origSymbol = global.Symbol;
+var hasSymbolSham = require('./shams');
+
+module.exports = function hasNativeSymbols() {
+	if (typeof origSymbol !== 'function') { return false; }
+	if (typeof Symbol !== 'function') { return false; }
+	if (typeof origSymbol('foo') !== 'symbol') { return false; }
+	if (typeof Symbol('bar') !== 'symbol') { return false; }
+
+	return hasSymbolSham();
+};
diff --git a/shams.js b/shams.js
@@ -0,0 +1,42 @@
+'use strict';
+
+/* eslint complexity: [2, 17], max-statements: [2, 33] */
+module.exports = function hasSymbols() {
+	if (typeof Symbol !== 'function' || typeof Object.getOwnPropertySymbols !== 'function') { return false; }
+	if (typeof Symbol.iterator === 'symbol') { return true; }
+
+	var obj = {};
+	var sym = Symbol('test');
+	var symObj = Object(sym);
+	if (typeof sym === 'string') { return false; }
+
+	if (Object.prototype.toString.call(sym) !== '[object Symbol]') { return false; }
+	if (Object.prototype.toString.call(symObj) !== '[object Symbol]') { return false; }
+
+	// temp disabled per https://github.com/ljharb/object.assign/issues/17
+	// if (sym instanceof Symbol) { return false; }
+	// temp disabled per https://github.com/WebReflection/get-own-property-symbols/issues/4
+	// if (!(symObj instanceof Symbol)) { return false; }
+
+	// if (typeof Symbol.prototype.toString !== 'function') { return false; }
+	// if (String(sym) !== Symbol.prototype.toString.call(sym)) { return false; }
+
+	var symVal = 42;
+	obj[sym] = symVal;
+	for (sym in obj) { return false; } // eslint-disable-line no-restricted-syntax
+	if (typeof Object.keys === 'function' && Object.keys(obj).length !== 0) { return false; }
+
+	if (typeof Object.getOwnPropertyNames === 'function' && Object.getOwnPropertyNames(obj).length !== 0) { return false; }
+
+	var syms = Object.getOwnPropertySymbols(obj);
+	if (syms.length !== 1 || syms[0] !== sym) { return false; }
+
+	if (!Object.prototype.propertyIsEnumerable.call(obj, sym)) { return false; }
+
+	if (typeof Object.getOwnPropertyDescriptor === 'function') {
+		var descriptor = Object.getOwnPropertyDescriptor(obj, sym);
+		if (descriptor.value !== symVal || descriptor.enumerable !== true) { return false; }
+	}
+
+	return true;
+};