Sum_Strings.js

/* ----------------------------------------------------------------------------------------

    Create a function that takes 2 integers in form of a string as an input, and outputs
    the sum (also as a string):

    Example: (Input1, Input2 -->Output)

    "4",  "5" --> "9"
    "34", "5" --> "39"
    "", "" --> "0"
    "2", "" --> "2"
    "-5", "3" --> "-2"
    
    Notes:

    If either input is an empty string, consider it as zero.

    Inputs and the expected output will never exceed the signed 32-bit integer limit
    (2^31 - 1)

---------------------------------------------------------------------------------------- */

/*
    parseInt():   parses a string argument and returns an integer of the specified radix

    Number.prototype.toString():   returns a string representing this number value
*/

function sumStr(a, b) {
  return (
    (parseInt(a) ? parseInt(a) : 0) + (parseInt(b) ? parseInt(b) : 0)
  ).toString();
}

/*
    Alternative solution
*/

function sumStr(a, b) {
  return String(Number(a) + Number(b));
}