The source code

    /**
     * @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 call.
     * @param {Object} scope (optional) The default scope (The <code><b>this</b></code> reference) in which the
     * function is called. If not specified, <code>this</code> will refer to the browser window.
     * @param {Array} args (optional) The default Array of arguments.
     */
    Ext.util.DelayedTask = function(fn, scope, args){
        var me = this,
        	id,
        	call = function(){
        		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. Remember that if no scope
         * is specified, <code>this</code> will refer to the browser window.
         * @param {Array} newArgs (optional) Overrides args passed to constructor
         */
        me.delay = function(delay, newFn, newScope, newArgs){
            me.cancel();
            fn = newFn || fn;
            scope = newScope || scope;
            args = newArgs || args;
            id = setInterval(call, delay);
        };

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