object-creation-patterns/object-constants.html

﻿<!doctype html>
<html lang="en">
	<head>
		<title>JavaScript Patterns</title>
		<meta charset="utf-8">
	</head>
	<body>
		<script>
			/* Title: Object Constants
			 Description: an implementation of a constant object provides set, inDefined and get methods
			 */

			var constant = (function () {
				var constants = {},
						ownProp = Object.prototype.hasOwnProperty,
						allowed = {
							string:1,
							number:1,
							boolean:1
						},
						prefix = (Math.random() + "_").slice(2);
				return {
					set:function (name, value) {
						if (this.isDefined(name)) {
							return false;
						}
						if (!ownProp.call(allowed, typeof value)) {
							return false;
						}
						constants[prefix + name] = value;
						return true;
					},
					isDefined:function (name) {
						return ownProp.call(constants, prefix + name);
					},
					get:function (name) {
						if (this.isDefined(name)) {
							return constants[prefix + name];
						}
						return null;
					}
				};
			}());

			// check if defined
			console.log(constant.isDefined("maxwidth")); // false

			// define
			console.log(constant.set("maxwidth", 480)); // true

			// check again
			console.log(constant.isDefined("maxwidth")); // true

			// attempt to redefine
			console.log(constant.set("maxwidth", 320)); // false

			// is the value still intact?
			console.log(constant.get("maxwidth")); // 480
		</script>
	</body>
</html>