Using Another Type's Methods

Sometimes an object needs methods from a type it isn't. The classic example: arguments inside a function looks like an array but isn't — so it lacks array methods.

function logArgs() {
  // arguments has no .join() — so we borrow it:
  const result = Array.prototype.join.call(arguments, ', ');
  console.log(result);
}
logArgs(1, 2, 3); // "1, 2, 3"

Modern Alternative: Array.from() or Rest Parameters

// Convert to a real array first
function logArgs(...args) {
  console.log(args.join(', ')); // args is already a real array
}

Method	Behavior
fn.call(thisArg, a, b)	Calls fn with this = thisArg
fn.apply(thisArg, [a, b])	Same but arguments as array
fn.bind(thisArg)	Returns a new permanently-bound function