Why does onscroll need (this) bound without parenthesis in this function? : I have made 2 functions on the onscroll function. One of which has extra parenthesis, and the other doesn't. Why does it not work with the extra parenthesis? Here is my code:

    var windowScroll = function() {

        var doesNotRun = function() {
            console.log('running1');
        };
        var doesRun = function() {
            console.log('running2');
        };
        window.onscroll = doesNotRun.bind(this)();
        window.onscroll = doesRun.bind(this);

    };

    windowScroll();

here is a link on codepen: http://codepen.io/marcoangelo/pen/KWdWem

any help to understand why Javascript does this would be great, thanks