[Breaking] conform to the es-shim API.

README.md

@@ -10,7 +10,9 @@ String.prototype.trimLeft <sup>[![Version Badge][npm-version-svg]][package-url]<
 
 [![browser support][testling-svg]][testling-url]
 
-An ES7 spec-compliant `String.prototype.trimLeft` shim. Invoke its "shim" method to shim `String.prototype.trimLeft` if it is unavailable.
+A spec-proposal-compliant `String.prototype.trimLeft` shim. Invoke its "shim" method to shim `String.prototype.trimLeft` if it is unavailable.
+
+This package implements the [es-shim API](https://github.com/es-shims/api) interface. It works in an ES3-supported environment and complies with the [spec](http://www.ecma-international.org/ecma-262/6.0/#sec-object.assign). In an ES6 environment, it will also work properly with `Symbol`s.
 
 Most common usage:
 ```js

implementation.js

@@ -0,0 +1,10 @@
+'use strict';
+
+var bind = require('function-bind');
+var replace = bind.call(Function.call, String.prototype.replace);
+
+var leftWhitespace = /^[\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF]*/;
+
+module.exports = function trimLeft() {
+	return replace(this, leftWhitespace, '');
+};

index.js

@@ -2,25 +2,17 @@
 
 var bind = require('function-bind');
 var define = require('define-properties');
-var replace = bind.call(Function.call, String.prototype.replace);
 
-var leftWhitespace = /^[\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF]*/;
+var implementation = require('./implementation');
+var getPolyfill = require('./polyfill');
+var shim = require('./shim');
 
-var trimLeft = function trimLeft() {
-	return replace(this, leftWhitespace, '');
-};
+var bound = bind.call(Function.call, getPolyfill());
 
-var boundTrimLeft = bind.call(Function.call, trimLeft);
-define(boundTrimLeft, {
-	shim: function shimTrimLeft() {
-		var zeroWidthSpace = '\u200b';
-		define(String.prototype, { trimLeft: trimLeft }, {
-			trimLeft: function () {
-				return zeroWidthSpace.trimLeft() !== zeroWidthSpace;
-			}
-		});
-		return String.prototype.trimLeft;
-	}
+define(bound, {
+	getPolyfill: getPolyfill,
+	implementation: implementation,
+	shim: shim
 });
 
-module.exports = boundTrimLeft;
+module.exports = bound;

package.json

@@ -6,7 +6,7 @@
 	"license": "MIT",
 	"main": "index.js",
 	"scripts": {
-		"test": "npm run lint && npm run tests-only&& npm run security",
+		"test": "npm run lint && es-shim-api --bound && npm run tests-only && npm run security",
 		"tests-only": "npm run test:shimmed && npm run test:module",
 		"test:shimmed": "node test/shimmed.js",
 		"test:module": "node test/index.js",
@@ -29,7 +29,8 @@
 		"trim",
 		"trimLeft",
 		"trimRight",
-		"polyfill"
+		"polyfill",
+		"es-shim API"
 	],
 	"dependencies": {
 		"define-properties": "^1.1.2",
@@ -41,7 +42,8 @@
 		"jscs": "^2.9.0",
 		"nsp": "^2.2.0",
 		"eslint": "^1.10.3",
-		"@ljharb/eslint-config": "^1.6.1"
+		"@ljharb/eslint-config": "^1.6.1",
+		"@es-shims/api": "^1.1.0"
 	},
 	"testling": {
 		"files": "test/index.js",

polyfill.js

@@ -0,0 +1,14 @@
+'use strict';
+
+var implementation = require('./implementation');
+
+module.exports = function getPolyfill() {
+	if (!String.prototype.trimLeft) {
+		return implementation;
+	}
+	var zeroWidthSpace = '\u200b';
+	if (zeroWidthSpace.trimLeft() !== zeroWidthSpace) {
+		return implementation;
+	}
+	return String.prototype.trimLeft;
+};

shim.js

@@ -0,0 +1,14 @@
+'use strict';
+
+var define = require('define-properties');
+var getPolyfill = require('./polyfill');
+
+module.exports = function shimTrimLeft() {
+	var polyfill = getPolyfill();
+	define(
+		String.prototype,
+		{ trimLeft: polyfill },
+		{ trimLeft: function () { return String.prototype.trimLeft !== polyfill; } }
+	);
+	return polyfill;
+};