javascript curry/partial function invokation for object functions

Question

I want a 'curry' like function - this kind of thing

function invoker (fn) {
    var slice = Array.prototype.slice,
        args = slice.apply(arguments, [1]);
    return function () {
       return fn.apply(null, args);
    };
}

But I want the user to be able to do

invoker(f)

or

invoker(foo.bar)

I cant find the correct magic incantation to do this. All the examples I see require the scope object to be passed in separately; which is error prone and not natural. IE

invokerx(foo.bar, foo)

IS there anyway to do this? I dont mind having 2 different functions

invokeG(f)
invokeO(foo.bar)

EDIT : clarification

'f' is a global scope function
'foo' is an object
'bar is a method on that object

IE I want this curry tool to work with'free' functions as well as with object functions.

Having to go

<curry function>(foo.bar,foo)

seems kinda clunky, I have have to say 'foo' twice

Saying "I want the user to be able to do invoker(f) or invoker(foo.bar)" doesn't describe what you want. Please describe in words the problem you're trying to solve. EDIT: Maybe you want the user to be able to bind a context to the function? — user113716
– user113716, Commented Oct 14, 2011 at 15:27

Brian Nickel · Accepted Answer · 2011-10-14 16:35:43Z

4

The first argument of apply is the this that is available to the function. Since you're passing null, this will get mapped to window.

The following modification will work:

function invoker (fn, target) {
    var slice = Array.prototype.slice,
        args = slice.apply(arguments, [2]);

    if(typeof fn === 'string')
        fn = (target || window)[fn];

    return function () {
       return fn.apply(target || null, args);
    };
}

// Either will work:
invoker(foo.bar, foo);
invoker('bar', foo);

// Any of these will work:
invoker(escape, null);
invoker(escape, window);
invoker('escape', null);
invoker('escape', window);

UPDATE Added a slight change to add support for name passing so you don't have to pass the object name twice.

UPDATE 2 Since we're currying, we need there to always be two arguments.

edited Oct 14, 2011 at 16:35

answered Oct 14, 2011 at 15:47

Brian Nickel

27.6k5 gold badges83 silver badges112 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

pm100 Over a year ago

right, but this requires the caller to use 2 different call signatures. My feeling is that invoker(foo.bar, foo) is redundant , I already said foo once

Brian Nickel Over a year ago

You know that, and I know that, but JavaScript doesn't know that. I'll add an alternate solution that doesn't require multiple instances of 'foo', but it will be less efficient.

pm100 Over a year ago

cmon brian, one more heroic effort and I am sure you can find a really nice solution. You are getting pretty close with the 'invoker('bar', foo), but we are still not quite there :-)

Eric Over a year ago

@pm100: Short of doing something horrible, like invoker('foo.bar'), that's as close as you can get

Brian Nickel Over a year ago

First off, it would only work if foo was a global variable. Second, it would require use of eval (scary/slow) or string parsing (slow). In practice, there are many examples of curry functions bound to objects and they all need a second parameter which often results in typing the object name twice. It's just how JavaScript works.

|

Eric · Accepted Answer · 2011-10-14 15:46:59Z

2

You can't. When you do invoker(foo.bar), invoker has no way of knowing that the argument is a member function of foo. Functions do not store their "owner", and invoker is just passed a reference to a function.

The closest you can get is to use function.bind(), like this:

invoker(foo.bar.bind(foo))

answered Oct 14, 2011 at 15:46

Eric

98.1k54 gold badges257 silver badges389 bronze badges

2 Comments

pm100 Over a year ago

I guess thats it, i wanted to find the 'owner' of the function. I am surprised that apply doesnt have some variant that allows this.

Brian Nickel Over a year ago

Actually, the .bind function is a currying function so you don't really need invoker here. var boundBar = foo.bar.bind(foo) is all you need. Otherwise you're currying a curried function. See: developer.mozilla.org/en/JavaScript/Reference/Global_Objects/…

Collectives™ on Stack Overflow

javascript curry/partial function invokation for object functions

2 Answers 2

6 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related