Make the codePointAt property non-enumerable

In environments where `Object.defineProperty` is not available, we fall back to exposing the polyfill as an enumerable property on `String.prototype`.

Author: mathiasbynens

codepointat.js

@@ -1,34 +1,45 @@
 /*! http://mths.be/codepointat v0.1.0 by @mathias */
 if (!String.prototype.codePointAt) {
-	String.prototype.codePointAt = function(position) {
-		'use strict';
-		if (this == null) {
-			throw TypeError();
-		}
-		var string = String(this);
-		var size = string.length;
-		// `ToInteger`
-		var index = position ? Number(position) : 0;
-		if (index != index) { // better `isNaN`
-			index = 0;
-		}
-		// Account for out-of-bounds indices:
-		if (index < 0 || index >= size) {
-			return undefined;
-		}
-		// Get the first code unit
-		var first = string.charCodeAt(index);
-		var second;
-		if ( // check if it’s the start of a surrogate pair
-			first >= 0xD800 && first <= 0xDBFF && // high surrogate
-			size > index + 1 // there is a next code unit
-		) {
-			second = string.charCodeAt(index + 1);
-			if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
-				// http://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
-				return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
+	(function() {
+		'use strict'; // needed to support `apply`/`call` with `undefined`/`null`
+		var codePointAt = function(position) {
+			if (this == null) {
+				throw TypeError();
+			}
+			var string = String(this);
+			var size = string.length;
+			// `ToInteger`
+			var index = position ? Number(position) : 0;
+			if (index != index) { // better `isNaN`
+				index = 0;
+			}
+			// Account for out-of-bounds indices:
+			if (index < 0 || index >= size) {
+				return undefined;
+			}
+			// Get the first code unit
+			var first = string.charCodeAt(index);
+			var second;
+			if ( // check if it’s the start of a surrogate pair
+				first >= 0xD800 && first <= 0xDBFF && // high surrogate
+				size > index + 1 // there is a next code unit
+			) {
+				second = string.charCodeAt(index + 1);
+				if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
+					// http://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
+					return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
+				}
 			}
+			return first;
+		};
+		if (Object.defineProperty) {
+			Object.defineProperty(String.prototype, 'codePointAt', {
+				'value': codePointAt,
+				'configurable': true,
+				'writable': true
+			});
+		} else {
+			String.prototype.codePointAt = codePointAt;
 		}
-		return first;
-	};
+	}());
 }

tests/tests.js

@@ -5,6 +5,7 @@ var assertThrows = assert['throws'];
 require('../codepointat.js');
 
 assertEquals(String.prototype.codePointAt.length, 1);
+assertEquals(String.prototype.propertyIsEnumerable('codePointAt'), false);
 
 // String that starts with a BMP symbol
 assertEquals('abc\uD834\uDF06def'.codePointAt(''), 0x61);