JS: How to Convert ES5 to ES2015
Here is a guide to convert ES5 to ES2015.
[see 2015 Features]
Follow this checklist, in order.
Variables and Constants
Change var to let
Change some let to const.
in any for-loop, put a let for the counter variable.
Use const as much as possible.
Functions
Remove any use of the arguments Object in function.
use function default values.
[see Function Argument Default Value]
use function rest parameter.
[see Function Rest Parameters]
If a function does not use the this keyword
[see this Binding]
, change it to Arrow Function
.
Change Function Blocks into Code Blocks
Remove the outmost function block of the from
(function (){body})()
that are just for creating local variables.
Replace it with {body} and let.
replace all
function f () {body}
form to
const f = function () {body}
You have to do this. Because we want to wrap a {} around our code. If you don't change function declaration into assignment form, you can't wrap the whole code into a block because
function declaration must happen only at top level.
Now, wrap whole file into a block by wrapping curly brackets {} around it.
Dealing with Unicode
Replace
String.fromCharCode
to
String.fromCodePoint
[see String.fromCharCode]
[see String.fromCodePoint]
Replace
charCodeAt
to
codePointAt
[see String.prototype.charCodeAt]
[see String.prototype.codePointAt]
Use Map
Rewrite some data structure that use object, to use Map.
[see the Map Object Tutorial]
Use Set
Rewrite some data structure that use array or object, to use Set.
[see the Set Object Tutorial]
Use Class
Rewrite constructor functions to use the class keyword. This would be a big complex change.
Better is to change the code to functional programing style.
[see Class]