function bind()

bind.js

/* partial implementation of Function.prototype.bind */
Function.prototype.bind || (Function.prototype.bind = function(/* context[,arg1,arg2...] */) {
  var fn = this;
  var args = Array.prototype.slice.call(this,arguments);//preset args
  var context = args.shift() || undefined;
  return function(){
    var args2 = args.concat( Array.prototype.slice.call(arguments) );//spec states any passed args should be appended to preset arguments.
    return fn.apply(context,args2);
  };
});