Closures With Es5 and Es6

Question

var add = function add(x, z) {
  if (z == undefined) {
    return function(y) {
      return x + y;
    }
  } else {
    return x + z
  }
}

The above code work well when i write code with arrow function not work

var add = add(x, z) => {
  if (z == undefined) {
    return (y) => {
      return x + y;
    }
  } else {
    return x + z
  }
}

Answer 1

Just a wrong syntax, as an arrow function should be declared like here

Replace add(x, z) => with (x, z) =>

Answer 2

Please remove the add key word, try to use const and let declaratio because them are block scoping, with var you allocate innecesary memori with the hositing of varables in JS

const add = (x, z) => {
  if (z == undefined) {
    return (y) => {
      return x + y;
    }
  } else {
    return x + z
  }
}

Answer 3

Nothing but wrong syntax. Have fun.

var add = (x, z) => {
  if (z == undefined) {
    return (y) => {
      return x + y;
    }
  } else {
    return x + z;
  }
}