I have a bunch of loops, for different arrays. I just need some counters. When I do this, jshint says my variables k and l are already defined. Should I move on to other letters of the alphabet? Is there a better way?

fors.js

for(var k in myarray){
	for(var l in myarray[k]){
		//do something with myarray[k][l]
	}
}

for(var k in someotherarray){
  for(var l in someotherarray[k]){
		//do something with someotherarray[k][l]
	}
}

//first loop... then
// re-re-re-reset
k = l = null;
for(k in someotherarray){
    for(l in someotherarray[k]){
        //do something with someotherarray[k][l]
    }
}

why not that? Note, I didn't put it through jslint (also, you should try jshint instead of jslint, it is less mean).

jshint report for:

var myarray = [],
    someotherarray = [];

for(var k in myarray){
  for(var l in myarray[k]){
    myarray[k][l]++;
  }
}

for(var k in someotherarray){
  for(var l in someotherarray[k]){
    someotherarray[k][l]++;
  }
}

JSHint Report:

/*jshint forin:true, noarg:true, noempty:true, eqeqeq:true, bitwise:true, strict:true, undef:true, unused:true, curly:true, browser:true, jquery:true, indent:4, maxerr:50 */

Errors:

Line 5: for(var l in myarray[k]){

The body of a for in should be wrapped in an if statement to filter unwanted properties from the prototype.

Line 4: for(var k in myarray){

The body of a for in should be wrapped in an if statement to filter unwanted properties from the prototype.

Line 11: for(var l in someotherarray[k]){

The body of a for in should be wrapped in an if statement to filter unwanted properties from the prototype.

Line 10: for(var k in someotherarray){

The body of a for in should be wrapped in an if statement to filter unwanted properties from the prototype.

Feel like some warnings are incorrect? You can configure JSHint to turn off some warnings. Read more in the documentation.

You can use function scoping. This gives an additional overhead of a closure, with attending allocations and deallocations, but it's quick and dirty, and a more universal solution that the resetting solution @SeanJA gives.

(function(){
for(var k in something) {
// ...
}
})();

(function(){
for(var k in somethingElse) {
// ...
}
})();

However, it's arguably better to just use variable names that have more meaning... somethingIdx, somethingElseIdx for instance. Or simply resetting. :)

You're over-thinking it, you just can't declare the variable every time:

var k;
var l;

for(k in myarray){
    for(l in myarray[k]){
        //do something with myarray[k][l]
    }
}

for(k in someotherarray){
  for(l in someotherarray[k]){
        //do something with someotherarray[k][l]
    }
}