JavaScript function name as a string...

Question

Hi,

I have the name of a function in JavaScript as a string, how do I convert that into a function pointer so I can call it later?

Depending on the circumstances I may need to pass various arguments into the method too...

EDIT I should note that some of the functions may take the form of namespace.namespace.function(args[...]);...

Answer 1

The answer to this other question shows you how to do that: http://stackoverflow.com/questions/39960/javascript-locals

Basically, you can say

window["foo"](arg1, arg2);

or as many others have suggested, you can just use eval:

eval(fname)(arg1, arg2);

although this is extremely unsafe unless you're absolutely sure about what you're eval-ing.

Answer 2

Two things:

• avoid eval, it's terribly dangerous and slow

• secondly it doesn't matter where your function exists, "global" -ness is irrelevant. x.y.foo() can be enabled through x.y['foo']() or x['y']['foo']() or even window['x']['y']['foo'](). You can chain indefinitely like this.

I <3 JS

Answer 3

Don't use eval unless you absolutely, positively have no other choice.

As has been mentioned, using something like this would be the best way to do it:

window["functionName"](arguments);

That, however, will not work with a namespace'd function:

window["My.Namespace.functionName"](arguments); // fail

This is how you would do that:

window["My"]["Namespace"]["functionName"](arguments); // succeeds

In order to make that easier and provide some flexibility, here is a convenience function:

function executeFunctionByName(functionName, context /*, args */) {
  var args = Array.prototype.slice.call(arguments).splice(2);
  var namespaces = functionName.split(".");
  var func = namespaces.pop();
  for(var i = 0; i < namespaces.length; i++) {
    context = context[namespaces[i]];
  }
  return context[func].apply(this, args);
}

You would call it like so:

executeFunctionByName("My.Namespace.functionName", window, arguments);

Note, you can pass in whatever context you want, so this would do the same as above:

executeFunctionByName("Namespace.functionName", My, arguments);

Hope that helps...

---

EDIT: Changed function name to be a bit more generic.

Answer 4

I need that too.

This seems to work when everything is defined at the top (window) level, but I've been unable to find the right syntax to make it work anywhere else. Anyone else know how to do that?...

// Define function...
function f(msg1,msg2) {
  alert(msg1+'\n'+msg2);
};

// Simulate function name existing within a string...
var a = 'f';

// Convert that string into a function ("pointer")
// by treating it as an array of one. Since arrays are just a
// special kind of object and all functions are objects, this
// makes the variable b reference the function 'f'...
var b = this[a];

// Execute function using the function "pointer"...
b('a is a '+typeof(a),'b is a '+typeof(b))