Passing functions to setTimeout in a loop: always the last value?

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This is the very frequently repeated “how do I use a loop variable in a closure” problem.

The canonical solution is to call a function which returns a function that’s bound to the current value of the loop variable:

var strings = [ "hello", "world" ];
var delay = 1000;
for(var i=0;i<strings.length;i++) {
    setTimeout(
        (function(s) {
            return function() {
                alert(s);
            }
        })(strings[i]), delay);
    delay += 1000;
}

The outer definition function(s) { ... } creates a new scope where s is bound to the current value of the supplied parameter – i.e. strings[i] – where it’s available to the inner scope.

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