jsbench003

A little tip if you like 'for' loops


  function f1() {
    var x=1;
    var array=[0,1,2,3,4,5,6,7,8,9];
    for (var z=0;z<600000;z++) {
      for (var y=0;y<array.length;y++) {
        x+=array[y]*z;
      }
    }
  }

  function f2() {
    var x=1;
    var array=[0,1,2,3,4,5,6,7,8,9];
    for (var z=0;z<600000;z++) {
      for (var y=0,yEnd=array.length;y<yEnd;y++) {
        x+=array[y]*z;
      }
    }
  }


function f1
the y loop verifies that y is < array.length before terminating
y < array.length
is tested for every loop cycle (600000 times in this test)

function f2
the y loop evalutes array.length only once... the end condition is y < yEnd


It is very common to see things of this kind
var array=[....]
for (var i=0;y<array.length;i++) {
but this is not good since array.length is evaluated at the end of each cycle for the entire loop.
So remember to create lookup vars if you are using objects or arrays inside loops.

f1 took:161ms f2 took:146ms [FF 3.5.2]


Conclusion: use this tecnique in Javascript 'for' loops
for (var i=0,iEnd=array.length;i<iEnd;i++) {