How can I pass methods in javascript?

Question

I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this:

a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }}

b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) })

c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) })

I want to know if there is a simpler way to pass methods attached to their original objects.

Answer 1

As long as you call the other method with its appropriate owner object, this will always refer to the correct owner.

Answer 2

You can define a "createDelegate" method for all functions:

Function.prototype.createDelegate = function(scope) {
    var method = this;
    return function() {
        return method.apply(scope, arguments);
    }
}

And then use like:

var myDelegate = myFunction.createDelegate(myScope);

calling "myDelegate" will execute "myFunction" with "this" pointing to "myScope" and the same arguments as passed to myDelegate

Answer 3

You can delegate if you like, or just call the object that lacks the method from the defined method scope-

instance.method.call(Other-Object/*,argument,...*/)

For example, if Array has a filter method, you can call it as if it were a method of a node list object.

var list=document.getElementsByTagName('p'), a=[], 

list= a.filter.call(list,function(itm){return itm.className=='sidebar'});