JS: How to Convert ES5 to ES2015
Here's a guide to convert ES5 to ES2015.
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.
〔►see JS: Function's “arguments” Object〕
〔►see JS: Function Parameters〕
use function default values.
〔►see JS: Function Argument Default Value〕
use function rest parameter.
〔►see JS: Function Rest Parameters〕
If a function does not use the this keyword, change it to arrow function.
〔►see JS: “this” Binding〕
〔►see JS: Arrow Function〕
Change Function Blocks into Code Blocks
Remove the outmost function block of the from
(function (){…})()
that are just for creating local variables.
Replace it with {…} and let.
replace all
function f () {…}
form to
const f = function () {…}
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 JS: String.fromCharCode〕
〔►see JS: String.fromCodePoint〕
Replace
charCodeAt
to
codePointAt
〔►see JS: String.prototype.charCodeAt〕
〔►see JS: String.prototype.codePointAt〕
Use Map
Rewrite some data structure that use object, to use Map.
〔►see JS: the Map Object Tutorial〕
Use Set
Rewrite some data structure that use array or object, to use Set.
〔►see JS: 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 JS: Class Tutorial〕