In this episode of Syntax, Scott and Wes talk about all the new stuff in ES2022 — what it is, why you might need it, and how to use it.

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Show Notes

04:50 - Regex indicies

New d flag in a regex
https://regex101.com/
This will tell you the indexes (indicies) of the regex matches
Handy if you need to highlight or replaces matches in a string
We can ask for the start and end positions of each matched capture group

07:16 - Class updates

Private fields
Properties and Methods to be kept private
Prefix them with a #
=Helpful for internal state and methods which should not be accessed directly or at all by external
In React how we have __INTERNTAL_NEVER USE THIS

  class ColorButton extends HTMLElement {   // All fields are public by default   color = "red"    // Private fields start with a #, can only be changed from inside the class   #clicked = false }  const button = new ColorButton() // Public fields can be accessed and changed by anyone button.color = "blue"  // SyntaxError here  console.log(button.#clicked) // Cannot be read from outside button.#clicked = true // Cannot be assigned a value from outside

Getters and setters introduced in es5
https://www.w3schools.com/js/js_object_accessors.asp

 class Person {   #hobbies = ['computers']   get #hobbiesGetter() { return this.#hobbies }     #getHobbies() { return this.#hobbies }     getHobbiesPublic() { return this.#hobbies } }  const scott = new Person();  scott.#getHobbies(); // doesn't work scott.getHobbiesPublic(); // works

09:07 - Class fields

This may seem super old because we have been polyfilling it forever
Right now if you want an instance field on a class, you need to declare it in the constructor
Now we can just declare them inside the class

10:36 - Static fields and methods

As above can also be static with the static keyboard
Works for methods too
- Explain what a static method is

13:17 - Top level await

So handy in modules. Need to pull in some data? Simple.

15:19 - Ergonomic brand checks for private fields

Used for checking if a private field on a class exists using the in keyword

16:00 - .at() method

Strings and arrays - we can use square brackets to reference items of the array
Super handy for grabbing the last item of an array

 // 🔥 New .at() method on arrays and strings  const toppings = ['pepperoni', 'cheese', 'mushrooms'];  // The old way to grab the last item toppings[toppings.length - 1]; // mushrooms  // using .at() method with a negative index toppings.at(-1); // mushrooms  // works with any index toppings.at(0); // pepperoni toppings.at(-2); // cheese  // and with strings! 'Meeting Room: B'.at(-1) // B

Why not use array[-1]?
We used to use slice(-1)
What about indexOf?

21:34 - Handy hasOwn method

https://github.com/tc39/proposal-accessible-object-hasownproperty

24:51 - Class static block

A static block allows you to run code before creating an optional static property during initialization
https://github.com/tc39/proposal-class-static-block

Links

https://github.com/tc39/proposals/blob/master/finished-proposals.md

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New to JavaScript — ES2022

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