Karatsuba Multiplication in JavaScript

karatsuba.js

/**
 * Karatsuba Multiplication
 * @param  {Number} x - first number
 * @param  {Number} y - second number
 * @return {Number} Multiply of x and y
 */
 
function karatsubaMulti(x, y) {

  let n = Math.min(('' + x).length, ('' + y).length);

  if(n == 1)
    return x * y;

  let tenpowhalfn = Math.pow(10, parseInt(n / 2));
  let tenpown = Math.pow(10, 2 * parseInt(n / 2));

  let a = parseInt(x / tenpowhalfn);
  let b = x % tenpowhalfn;
  let c = parseInt(y / tenpowhalfn);
  let d = y % tenpowhalfn;

  let caller = arguments.callee;

  return tenpown * caller(a, c) + tenpowhalfn * (caller(a, d) + caller(b, c)) + caller(b, d);
}

IF you get the error

TypeError: 'caller', 'callee', and 'arguments' properties may not be accessed on strict mode functions or the arguments objects for calls to them

All you have to do is remove line 23, 'let caller = .... ' and change the return to

  return tenpown * karatsubaMulti(a, c)
    + tenpowhalfn * (karatsubaMulti(a, d)
    + karatsubaMulti(b, c))
    + karatsubaMulti(b, d)