Question

I’m trying to have a function that is passed a function and calls it with a set of args. For example:

function foo(func, args) {
  return func(args);
}

However, I don’t know how many elements might be in args, and func should be able to be an arbitrary function that takes any number of args. How do I deal with this?

Also say I wanted to store the functions passed to foo and only call them if they hadn’t been called before.

Can I just do something like:

var calledFuncs = [];
function foo(func, args) {
  if(calledFuncs.indexOf(func) === -1) {
    calledFuncs.push(func);
    return func(args);
  }
}

Thanks, I’m a bit new to functional programming in JavaScript.

Answer 1

You’re looking for func.apply:

• the first argument is the context aka this value. You don’t want to change this, so pass it through.
• the second argument is an array containing the arguments, which can of course be of dynamic length.

So you could do this:

return func.apply(this, args);

You seem to have a fine approach to your second issue (with the func(args) replaced). You may want to store the return value of called functions, though, since foo now returns undefined for any calls except the first.