Any examples of a non-trivial and useful example of the 'with' keyword?

Question

I still find the with keyword a bit...enigmatic.

Briefly, with behaves like this:

with (obj) {
    // do stuff
}

This adds obj to the head of the scope chain and then executes the with-block. When the block is finished it removes obj from the head of the scope chain.

According to MDC, this allows you to do stuff like

var a, x;
var r = 10;
with(Math) {
    a = PI * r * r;
    x = r * cos(PI / 2);
}

So I can reference properties of Math -- like PI -- directly, without saying Math.PI. Which is fine, but kind of useless.

Can anyone provide an example of an interesting usage of with?

Answer 1

An alternative to the standard closure solution using functions inside of a for loop:

<a  href="#">blah</a><br>
<a  href="#">blah</a><br>
<a  href="#">foo</a><br>
<script>
    (function() {
    var anchors = document.getElementsByTagName('a');
        for ( var i = anchors.length; i--; ) {
            var link = anchors[i];
            with ({ number: i }) {
                link.onclick = function() {
                    alert(number);
                };
            }
        }
    })();
</script>

Credit to nlogax for providing a solution which I pretty much ripped off: Javascript infamous Loop issue?

Here's the standard solution:

<script>
    (function() {
    var anchors = document.getElementsByTagName('a');
    for ( var i = anchors.length; i--; ) {
        var link = anchors[i];
        (function(i) {
            link.onclick = function() {
                alert(i)
            }
        })(i);
    }
    })();
</script>