Nodejs: how to clone an object

Object.assign hasn't been mentioned in any of above answers.

let cloned = Object.assign({}, source);

If you're on ES6 you can use the spread operator:

let cloned = { ... source };

Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign

For utilities and classes where there is no need to squeeze every drop of performance, I often cheat and just use JSON to perform a deep copy:

function clone(a) {
   return JSON.parse(JSON.stringify(a));
}

This isn't the only answer or the most elegant answer; all of the other answers should be considered for production bottlenecks. However, this is a quick and dirty solution, quite effective, and useful in most situations where I would clone a simple hash of properties.