Simple implementation of a curry for teaching purposes

curry.js

/*
 * curry(fn: Function) => Function
 * Simple implementation of currying a function
 * Drawbacks:
 * - Cannot be reused as stored args is mutable
 * - Cannot use placeholders
 * - Will not check argument overflow
 */
function curry(fn) {
  var arity = fn.length; // check the arity of the given function
  var args = [];  // store all arguments here
  function curried() { // the curried function
    args = args.concat(Array.prototype.slice.call(arguments));
    if (arity <= args.length) {
      return fn.apply(null, args); // call the function with all the arguments
    }
    return curried; // otherwise return the curried function to be given more arguments
  }
  return curried;
}

curry_test.js

var example = (a, b, c) => a + b + c;

console.log(curry(example)(1)(2));    // => function
console.log(curry(example)(1, 2));    // => function

console.log(curry(example)(1)(2)(3)); // => 6
console.log(curry(example)(1)(2, 3)); // => 6
console.log(curry(example)(1, 2)(3)); // => 6
console.log(curry(example)(1, 2, 3)); // => 6