Question

Here is a demo

Specifically, this is the part I find confusing:

$('.red').change(function(){
    pix = imageData.data;

    for(var i = 0, n = pix.length; i < n; i += 4){
        var green = 1, blue = 1;
        pix[i] = pix[i] * $(this).val();
        pix[i + 1] = pix[i + 1] * green;
        pix[i + 2] = pix[i + 2] * blue;
    }
    context.putImageData(imageData, 0, 0);
});

How is it that modifying pix (which should be in the global scope) modifies the imageData object? Javascript does not directly support pointers.

Answer 1

Javascript does not directly support pointers.

No, but it is a reference, which has very similar semantics. You’re not creating a copy in that assignment. Objects are passed by reference, primitive types by value.