Javascript: closure of loop?

Question

I would like to do the something along the following:

for (var i = 0; i < 10; ++i) {
    createButton(x, y, function() { alert("button " + i + " pressed"); }
}

The problem with this is that I always get the final value of i because Javascript's closure is not by-value.
So how can I do this with javascript?

Answer 1

One solution, if you're coding for a browser that uses JavaScript 1.7 or higher, is to use the let keyword:

for(var i = 0; i < 10; ++i) {
    let index = i;
    createButton(x, y, function() { alert("button " + index + " pressed"); }
}

From the MDC Doc Center:

The let keyword causes the item variable to be created with block level scope, causing a new reference to be created for each iteration of the for loop. This means that a separate variable is captured for each closure, solving the problem caused by the shared environment.

Check out the MDC Doc Center for the traditional approach (creating another closure).