Wednesday, October 5, 2011

bind, apply, and call trap

quick one out of ECMAScript ml

// used to trap function calls via bind
invoke =,
// normal use cases
bind = invoke.bind(invoke.bind),
apply = bind(invoke, invoke.apply),
call = bind(invoke, invoke)

What Is It

This is a way to trap native functions method in a handy way. Used in a private scope, it can address these methods once so that we can rely nobody can possibly change them out there for some script injection and only if we are sure the script has been loaded at the very beginning.

How To Use Them

Here few examples:

// secure hasOwnProperty
var hasOwnProperty = bind(invoke, {}.hasOwnProperty);
// later on
hasOwnProperty({key:1}, "key"); // true
hasOwnProperty({}, "key"); // false

// direct slice
var slice = bind(invoke, [].slice);
slice([1,2,3], 1); // 2,3
slice(arguments); // array

// direct call
call([].slice, [1,2,3], 1); // 2,3
// direct apply
apply([].slice, [1,2,3], [1]); // 2,3

// bound method
var o = {name:"WebReflection"};
o.getName = bind(
// the generic method
function () {
// the object
o.getName(); // WebReflection
That's pretty much it, except if we don't trust native Function.prototype, we should not trust anything else as well so maybe it's good to use these shortcuts just because they are handy ;)

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