Javascript - scope of nested for loop index

Question

I remember variables are function scoped in Javascript. But, how is the behavior if I redefine the local variable in a loop. One common use case is nested loops. In the bel

Answer 1

There's no block level scope in JS.

But if it's utmost necessary to have/re-declare the same variable name in your code, you can do:

function loopIt(arr, fn, scope) {
    for (var i = 0, len = arr.length; i < len; i++) {
        fn.call(scope || this, arr[i], i, arr);
    }
}

And use it like:

var firstArr = ["a", "b"];
var secondArr = ["c", "d"];

loopIt(firstArr, function(item, i) {
    var msg = "Hey it's '" + item + "'";
    console.log(msg);

    // if you want access to the parent scope's var
    var scopedItem = item;

    loopIt(secondArr, function(item, i) {
        var msg = "Hello it's '" + item + "' in '" scopedItem + "'";
        console.log(msg);
    });
});

That will give us results of:

Hey it's 'a'
Hello it's 'c' in 'a'
Hello it's 'd' in 'a'
Hey it's 'b'
Hello it's 'c' in 'b'
Hello it's 'd' in 'b'