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Rediscovering JavaScript: ES6, ES7 & ES8

Perils of Mutability

Understand the perils of mutable variables in JavaScript through examples that highlight how changes to outer scope variables can lead to unexpected results. Learn why favoring immutability with const helps reduce bugs and makes code easier to maintain.

We'll cover the following...

let does not permit the redefinition of variables, but it allows changing the value held in the variable.

Mutable data example in JavaScript

Without executing it, look at the following code to determine what the output will be.

Javascript (babel-node)
'use strict';
let factor = 2;
let product = function(number) { 
  return number * factor;
};
factor = 0; 
console.log(product(4));

Show the code to your colleagues nearby or far away. What good is technology if you can’t use it to bother someone with a coding problem? Ask them to ...