タイマーを使ってコストのかかる関数を遅延実行させる

 function swap(items, firstIndex, secondIndex) {
     var temp = items[firstIndex];
     items[firstIndex] = items[secondIndex];
     items[secondIndex] = temp;
 }
 
 function bubbleSort(array, onComplete) {
     var pos = 0;
     (function () {
         var j;
         for (j = array.length; j > pos; j--) {
             if (array[j] < array[j - 1]) {
                 swap (array, j, j - 1);
             }
         }
         pos++;
         if (pos < array.length) {
             setTimeout(arguments.callee, 500);
         } else {
             onComplete(array);
         }
     })();
 }
 var array = [3,1,4,2];
 bubbleSort(array, function (v) { console.log(v)} );

 function chunk(array, process, context) {
     var items = array.concat();
     setTimeout(function () {
         var item = items.shift();
         process.call(context, item);
         if (items.length > 0) {
             setTimeout(arguments.callee, 100);
         }
     }, 100);
 }
 
 var obj = { items : [] };
 var items = [ 1,2,3 ];
 chunk(items, function (value) {
     this.items.push( value * 10);
 }, obj);
 console.log(obj.items);

出典

http://www.slideshare.net/nzakas/writing-efficient-javascript