JavaScript “with” statement – usages

I ran into the JavaScript with statement the other day, here are some examples of its usage:

Problem with variable scope and closures. In the below code, when the function runs, “i” will not be the same as the value it was when the function was created:

for(var i = 0; i < 3; ++i){
		setTimeout(function() {
                     alert(i);
                }, 100);	
}

This doesn’t fix it either:

var num = 0;
for(var i = 0; i < 3; ++i){
	num = i;
		setTimeout(function() {
                     alert(num);
                }, 100);	
}

We can get our desired output using with

for(var i = 0; i < 3; ++i){
	with({num: i}){
		setTimeout(function() {
                     alert(num);
                }, 100);	
        }
}

Note: I agree with this blog post about with considered harmfull. The above usage is different to this blog post.