JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://getfirebug.com/firebug-lite-debug.js"></script>

JavaScript

var obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3"
};
var obj1 = {
  key4: "value4",
  key5: "value5",
  key6: "value6"
};
Object.assign(obj, obj1);
console.log(obj);