how to add property to string js code example

Example 1: add property to string js

const s = 'Hello world!'
  s.user = 'Jack';     // no error if used without 'use-strict'

  console.log(s.user); // undefined

Example 2: add property to object javascript

let yourObject = {};

//Examples:
//Example 1
let yourKeyVariable = "yourKey";
yourObject[yourKeyVariable] = "yourValue";

//Example 2
yourObject["yourKey"] = "yourValue";

//Example 3
yourObject.yourKey = "yourValue";