Transform an array into a comma separated variables WITHOUT apply

Question

I am attempting to reimplement apply for practice. I figured out a naive solution to execute a function in the context of an object by temporarily decorating that function on the object and then deleting it after. But I can't figure out how to pass the fn comma separated arguments when I invoke it because they are in array form.

How can I transform an array into a comma separated variables WITHOUT apply, call, or bind?

function apply(fn, context, args) {
  context.fn = fn;
  var result = context.fn();
  delete context.fn;
  return result;
}

function add(a,b) {
  return a + b + this.num;
}

console.log(apply(add, {num: 10}, [3, 4])); //17

EDIT:

I do NOT want my values split into a string. I want my values split into comma separated form. This is essentially what apply does under the hood when you pass it an array.

Answer 1

Try the following:

[1,2,3,4,5].join(",")

Answer 2

You can do so in ES6 with the help of the spread operator:

console.log(...myArray);

At the time of this writing, this feature is supported by FF37 and transpilers such as Traceur and Babel.

Another way of doing it would be by currying the function and looping to pass the arguments. Something along the lines of:

myArray.forEach(curriedConsoleLog);

That said, I don't see harm in just using apply.

Answer 3

As your function can only receive two arguments this would work :

function apply(fn, context, args) {
  context.fn = fn;
  var result = context.fn(args[0],args[1]);
  delete context.fn;
  return result;
}

function add(a,b) {
  return a + b + this.num;
}

console.log(apply(add, {num: 10}, [3, 4]));

Answer 4

function apply(fn, context, args) {
    context.fn = fn;
    while (args.length) {
        context.fn = context.fn(args.shift());
    }
    return context.fn;
}

function cubus(a) {
    return function (b) {
        return function (c) {
            return a * b * c / this.num;
        }
    }
}

function add(a) {
    return function (b) {
        return a + b + this.num;
    }
}

document.write(apply(add, { num: 10 }, [3, 4]));
document.write('<br>');
document.write(apply(cubus, { num: 10 }, [3, 4, 5]));

have a look at What is 'Currying'?