JS closures and anonymous functions...

closure-example.js

//jquery
var a_s = $('a');
a_s.each(function(i, e) {
    (function(a, num) {
        a.on('click', function(e) {
            e.preventDefault();
            console.log('I\'m number ' + num);
        });
    })($(e), i);
});

//javascript
var a_s = document.getElementsByTagName('a');
for (var i = 0, j = a_s.length; i < j; i++) {
    var el = a_s[i];
    (function(element, number) {
        element.addEventListener('click', function(e) {
            e.preventDefault();
            alert('I\'m number ' + number);
        }, false);
    })(el, i);
}