Dealing with duplicate declaration warning for loop variables

Question

Consider the following code:

for (var i=0; i<100; i++) {
    // your code here
}
// some other code here
for (var i=0; i<500; i++) {
    // custom code her         


        

Answer 1

I recommend enclosing your loops within self-executing functions whose names tell you what the loop is doing. This effectively gives block scope to the loop. For example:

var users = response['users']
;(function appendUsers(){
    for (var i = 0; i < users.length; i++) {
        var user      = users[i]
        var userEmail = user['email']
        var userId    = user['id']
        /* etc */ 
    }
})() // appendUsers

If you do this:

var i
for (i = 0; i < someVar.length; i++) {
    for (i = 0; i < someOtherVar.length; i++) {
        // This is a bug that a validator will not notice.
    }
}

On the other hand:

for (var i = 0; i < someVar.length; i++) {
    for (var i = 0; i < someOtherVar.length; i++) {
        // This is a bug that a validator will warn you about.
    }
}
for (var i = 0; i < yetAnotherVar.length; i++) {
    // It will also warn you about this, but so what?
}

You can stop using i as an iterator:

for (var companyIndex = 0; companyIndex < companies.length; companyIndex++) {
    var company = companies[companyIndex]
}

If you're using jQuery anyway, you can use its jQuery.each() method:

$.each(someVar, function(i, value){
    // etc
})

You can't use Array.prototype.forEach() if you want IE8 and earlier to work, unless you add the Polyfill code or similar.