Function multiply

javascript/0043-multiply-strings.js:9–19

(num1, num2)

 * @return {string}
 */
var multiply = (num1, num2) => {
    const isZero = num1 === '0' || num2 === '0';
    if (isZero) return '0';

    const buffer = initBuffer(num1, num2); /*               | Space (N + M) */

    multiplication(num1, num2, buffer); /* Time O(N * M) */
    removeLeadingZero(buffer); /* Time O(N + M) | Time O(N + M)*/

    return buffer.join(''); /* Time O(N + M) | Space O(N + M) */
};

var initBuffer = (num1, num2) => {
    const size = num1.length + num2.length;