Question

I have seen both….variable declaration in or before the for statement. Which is better? Here is an example snippet.

MC.initAll = function() {
    var iterate = [MC, Su], 
        l = iterate.length, 
        i, 
        key;
    for( i = 0; i < l; i++ ) {
        for( key in iterate[i]) {
            if( iterate[i].hasOwnProperty(key) && iterate[i][key].hasOwnProperty("init") ) {
                iterate[i][key].init();
            }
        }
    }
}

Pros of putting at top of function outside the for statement:

• less code due to using the same var statement
• already hoisted , js does not have to
• internal working made more explicit
• will pass jshint.com

Pros of putting in the for statement

• easy visual inspect to verify declaration took place in function

Answer 1

It is personal style. Which is “better” is purely a matter of opinion. The javascript interpreter will hoist all variable definitions to the start of the variable block no matter where the var statement appears.

I personally like to put my var in the for loop just so there is no accidental forgetting and using an implicit global variable, but that’s just a personal style choice. I know others like all variables declared explicitly at the start of the function.