Javascript: Basic for loop is not working -

is there reason why following not work:

for (i=0;i < somearray.length;i++) {     if (somearray[i].indexof("something") !== -1) {         //do here     } } 

the basic "for" loop possible. doesn't work. on first line (declaration of loop, not inside loop), "uncaught reference error; not defined."

i have page open in 1 chrome tab, , earlier version of page open in tab. in other tab, loop works fine; in first tab, code throws error.

edit - july 2 2015

the response strict mode helpful. after reading bit , going through code i've got handle on what's going on.

the confusing bit both versions of code this, minor differences (requirejs module):

define(     'viewmodels/someviewmodel',     ['dependency1', 'dependency2', 'dependency3'],     function(dep1, dep2, dep3) {          "use strict";          function someviewmodel(arg1, arg2) {             var self = this;             self.initialize();              self.removerefinement = function(refinementstring) {                 var refinementarray = refinementstring.split("&");                  (i=0;i < navigationarray.length;i++) { //<-- error                  }             }         }     } ); 

one version throws reference error. 1 doesn't.

this large web application many other pages , javascript files. thing think of in 1 version of code, maybe had been inadvertently globally defined somewhere else in app, strict mode wasn't enabled. after running breakpoint , checking "window" see that's what's happening.

thanks =d

if in strict mode, you'll error uncaught reference error; not defined. if you're not in strict mode, won't error.

this throw error

'use strict'  var somearray = ['aaa', 'bbb', 'ccc'];    (i=0;i < somearray.length;i++) {    console.log(i)    if (somearray[i].indexof("something") !== -1) {      //do here    }  }

this won't

var somearray = ['aaa', 'bbb', 'ccc'];    (i=0;i < somearray.length;i++) {    console.log(i)    if (somearray[i].indexof("something") !== -1) {      //do here    }  }