ES6 and beyond

I’ve just completed the Udacity Google Developer Challenge Scholarship, which covered Mobile Web development, Service Workers, IndexedDB and ES6.

I will go through some of the ES6 syntax and functions I learned on the course, will cover Service Workers and IndexedDb in a separate post.

ES6, Harmony, ES2015 are all different names for all the same thing Javascript. This major update has changed the way we write Javascript and it has also introduced some new builtins.

Var and Hoisting

There are now two ways to write variables, previously when you we writing Javascript you would declare a variable using the keyword var.

So why the change from var,

Variables declared with the var keyword were hoisted at runtime, which means they were raised to the top of the function scope.

Javascript is basically putting function declarations in memory before it runs the code. This allows you to use a function in Javascript before you decalre it in your code.

You can still declare variables using the `var’ keyword when you want a variable to be global, however this is now seen as bad practice.

Let and Const

Variables declared with let can be reassigned

let instructor = 'James';
instructor = 'Richard';

However they can’t be redeclared in the same scope.

{
let instructor = 'James';
instructor = 'Richard';

let instructor = 'Dave';
}

this would fail.

With const the rules are different, a variable declared with const must be assigned an initial value, but can’t be redeclared in the same scope, and can’t be reassigned.

const INSTRUCTOR = 'James';