delayedtask.js

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/*
 * Ext JS Library 3.0 Pre-alpha
 * Copyright(c) 2006-2008, Ext JS, LLC.
 * [e-mail]
 * 
 * http://extjs.com/license
 */

/**
 * @class Ext.util.DelayedTask
 * <p> The DelayedTask class provides a convenient way to "buffer" the execution of a method,
 * performing setTimeout where a new timeout cancels the old timeout. When called, the
 * task will wait the specified time period before executing. If durng that time period,
 * the task is called again, the original call will be cancelled. This continues so that
 * the function is only called a single time for each iteration.</p>
 * <p>This method is especially useful for things like detecting whether a user has finished
 * typing in a text field. An example would be performing validation on a keypress. You can
 * use this class to buffer the keypress events for a certain number of milliseconds, and
 * perform only if they stop for that amount of time.  Usage:</p><pre><code>
var task = new Ext.util.DelayedTask(function(){
    alert(Ext.getDom('myInputField').value.length);
});
// Wait 500ms before calling our function. If the user presses another key 
// during that 500ms, it will be cancelled and we'll wait another 500ms.
Ext.get('myInputField').on('keypress', function(){
    task.{@link #delay}(500); 
});
 * </code></pre> 
 * <p>Note that we are using a DelayedTask here to illustrate a point. The configuration
 * option <tt>buffer</tt> for {@link Ext.util.Observable#addListener addListener/on} will
 * also setup a delayed task for you to buffer events.</p> 
 * @constructor The parameters to this constructor serve as defaults and are not required.
 * @param {Function} fn (optional) The default function to timeout
 * @param {Object} scope (optional) The default scope of that timeout
 * @param {Array} args (optional) The default Array of arguments
 */
Ext.util.DelayedTask = function(fn, scope, args){
    var me = this,
    	NULL = null,
    	id = NULL, 
    	_delay, 
    	_time,    	    	
    	call = function(){
	        var now = new Date().getTime();
	        if(now - _time >= _delay){
	            clearInterval(id);
	            id = NULL;
	            fn.apply(scope, args || []);
	        }
	    };
	    
    /**
     * Cancels any pending timeout and queues a new one
     * @param {Number} delay The milliseconds to delay
     * @param {Function} newFn (optional) Overrides function passed to constructor
     * @param {Object} newScope (optional) Overrides scope passed to constructor
     * @param {Array} newArgs (optional) Overrides args passed to constructor
     */
    me.delay = function(delay, newFn, newScope, newArgs){
        if(id && delay != _delay){
            this.cancel();
        }
        _delay = delay;
        _time = new Date().getTime();
        fn = newFn || fn;
        scope = newScope || scope;
        args = newArgs || args;
        if(!id){
            id = setInterval(call, _delay);
        }
    };

    /**
     * Cancel the last queued timeout
     */
    me.cancel = function(){
        if(id){
            clearInterval(id);
            id = NULL;
        }
    };
};