Question

JavaScript is purported to have first-class functions, so this seems like the following ought to work:

var f = document.getElementById;
var x = f('x');

But it fails on all browsers, with a different cryptic error message on each one. Safari says “Type error”. Chrome says “Illegal invocation”. Firefox says “Could not convert JavaScript argument”.

Why?

Answer 1

Because in JavaScript functions arent bound to context (this). You may use bind():

var f = document.getElementById.bind(document);