Despite of various Syntax error

1) string enclosed by ‘ and ’ is not valid javascript string, similarly with “ and ”. Use either " or '.

2) variable should be declared with let not Let.

SOLUTION

You can take advantage of closure and Higher order function(HOF) here

function alertMyPreviousParam(arg) {
  let last = arg;
  return function (curr) {
    console.log(last);
    last = curr;
    return alertMyPreviousParam(curr);
  };
}

let y = alertMyPreviousParam("1");

let z = y("2");
// show output as  1

let a = z("3");
// show output as 2

let b = a("ra");
// show output as 3

let c = b("z");
// show output as ‘ra’,

You’ll want to look into closures. Here’s an example:

let var = null
let next = null
const myFunc = (newnext) => {
  var = next
  next = newnext
  return var
}

Sorry for the formatting, I’m on mobile

the function alertMyPreviousParam, returns a new function, and outputs the previous input. This can be achieved as follows:

let alertMyPreviousParam = (x) => (y) => {
  console.log(x);
  return alertMyPreviousParam(y);
}