jsbench001

it is right to declare a variable inside a loop? or is it better to declare it outside?


  function f1() {
    var a=25;
    var x; //we declare x outside the loop
    for (var z=0;z<2900000;z++) {
      x=a+z;
    }
  }

  function f2() {
    var a=25;
    for (var z=0;z<2900000;z++) {
      var x=a+z; //x is declared inside the for loop
    }
  }



function f1
var x is declared once

function f2
var x is declared and re-declared for every loop cycle


It seems that moving the var outside the loop keeps the loop faster.

But this is not always noticeable:
f1 took:12ms f2 took:13ms [FF 3.5.1]
Sometimes values are equal...
f1 took:13ms f2 took:13ms [FF 3.5.1]
sometimes f2 is faster...:
f1 took:13ms f2 took:11ms [FF 3.5.1]
f1 took:13ms f2 took:12ms [FF 3.5.1]


Conclusion: you decide. But personally I think it is better to declare variables outside loops.