Java Map in JavaScript - An object that maps keys to values.

JavaScript Map

/**
* An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.
* For those familiar with the Java programming language, this is similar to a HashMap; it implements most of the 
* methods defined by Java's java.util.Map interface.
*   
* @constructor
* @version 1.1.0
* @author cody@base22.com Burleson, Cody
*/
function Map() {

	this.dict = {};

	/**
	* Returns the number of key-value mappings in this map.
	* @method
	*/
	this.size = function() {
		return Object.keys(this.dict).length;
	};

	/**
	* Returns true if this map contains no key-value mappings.
	* @method
	*/
	this.isEmpty = function() {
		return Object.keys(this.dict).length == 0;
	};

	/**
	* Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. 
	* @method
	*/
	this.get = function(key){
		return this.dict[key];
	};

	/**
	* Returns true if this map contains a mapping for the specified key.
	* @method
	*/
	this.containsKey = function(key){

		if( this.get(key) !== undefined) {
			return true;
		} else {
			return false;
		}

	};

	/**
	* Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
	* @method
	*/
	this.put = function(key,value) {
		this.dict[key] = value;
	};

	/**
	* Removes the mapping for the specified key from this map if present.
	* @method
	*/
	this.remove = function(key) {
		'use strict';
		delete this.dict[key];
	};

	/**
	* Removes all of the mappings from this map. The map will be empty after this call returns.
	* @method
	*/
	this.clear = function(){
		this.dict = {};
	};
	
	/**
	 * Executes the given callback for each entry in this map until all entries have been processed.
	 * The given callback will be passed a map entry as parameter. So, for example...
	 *
	 * function myCallback(mapEntryItem) {
	 * 		console.log('I will process this item: ' + mapEntryItem.text);
	 * }
	 *
	 * myMap.forEach(myCallback);
	 *
	 * @method
	 */
	this.forEach = function(callback) {
		var len = this.size();
		for (i = 0; i < len; i++) {
			var item = this.get( Object.keys(this.dict)[i] );
			callback(item);
		}
	}

}

JavaScript Map Tests

/** 
* =============================
* Map Test Cases
* =============================
*/

/**
* Useful for unit testing JavaScript, this method asserts that the given condition is true. 
* If the given condition is not true, an optionally provided message is logged or 'Assertion failed.'
* @method
*/
function assert(condition, message) {
    if (!condition) {
        console.error(message) || console.error('Assertion failed');
    } else {
    	console.log("-- PASS");
    }
}

// Instantiate a new Dictionary object...
var myMap = new Map();

// Test that isEmpty returns true at this point
assert( myMap.isEmpty() );

// Test that size is zero at this point
assert( myMap.size() == 0 , "size should be zero before any entries have been put into the lookup table.");

// Put a sim0le string value in the dictionary and then test for it

myMap.put('key1','http://value1?dt=2014_06_01&dummy=true');

// Now let's test adding a different kind of object...
var testObj = {prop1:"Hello", prop2:" World!"};
myMap.put('key2',testObj);

// Test that size now equals one
assert( myMap.size() == 2, "size should be 2 after adding 2 entries.");

var ref = myMap.get('key2');

// Test that ref was fetched from the dictionary
assert( ref !== undefined , "ref should not be undefined; it should be a reference to testObj");

// Test a property of the fetched object; just to show there is support for more than just string types
assert( ref.prop1 == 'Hello' , "ref.prop1 should equal 'hello' ");

// Show that containsKey is false when there is no matching key
assert( myMap.containsKey('notReal') == false, "containsKey('notReal') should return false; no such object is in the lookup table.");

// Show that containsKey is true when there is a matching object found
assert( myMap.containsKey('key2') == true, "containsKey('key2') should return true; that object is in the lookup table.");

// Now, we remove an item to test the remove() method
myMap.remove('key1');
assert( myMap.size() == 1 , "size should be 1 after removing item under 'key1'.");

// Finally, test the clear()
myMap.clear();
assert( myMap.size() == 0 , "size should be 0 after clearing lookup table.");

Awesome Explanation!

Awesome Explanation!

Thank you! But, please be advised that maps are now available as a part of the ECMAScript 2015 (ES6) standard. See: Map - JavaScrip, MDN