Question

I want to delegate several methods from one JavaScript-Object to another. So i thought about using metaprogramming to not have several methods be defined just as delegates. So far i ended up with this method:

function delegate_to(_method, _obj) {
  return function(_args) { // One parameter, what's about multiple parameters?
    return _obj[_method](_args)
  }
}

So as an example-code how it should work:

var that = {}
var delegate = {}
that.foo = function(_message) { console.log("foo: " + _message) }
that.bar = function(_message) { console.log("bar: " + _message) }
that.baz = function(_message) { console.log("baz: " + _message) }

function delegate_to(_method, _obj) {
  return function(_args) { // One parameter, what's about multiple parameters?
    return _obj[_method](_args)
  }
}

['foo', 'bar', 'baz'].forEach(function(method) {
  delegate[method] = delegate_to(method, that)
})

delegate.foo('Hello JS') // foo: Hello JS
delegate.bar('Hello JS') // bar: Hello JS
delegate.baz('Hello JS') // baz: Hello JS

The code does work, but what’s if i want to delegate a method that does have more than one parameter? How about n parameters? Is it possible to change the code to have any number of parameters? Is this running in any browser?

Regards, Rainer

Answer 1

Function has methods called ‘apply’ to pass variable number of parameters as an array. Refer MDC:Function.apply

You can convert all the parameters passed to a function into an array by
Array.prototype.slice.call(arguments, 0)

Using these two principals, I have modified you code to taken multiple number of parameters. See the JSBin http://jsbin.com/iwiwix/3/watch

Relevant code extract:

delegate.foo('Hello JS', "from foo"); // foo: Hello JS



function delegate_to(_method, _obj) {
  return function() {
    var argArray =  Array.prototype.slice.call(arguments, 0);
    return _obj[_method].apply(_obj, argArray);
  };
}



that.foo = function() { console.log("foo: " + arguments[0] + ' ' + arguments[1]); };