New to JavaScript — ES2022


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
  • 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 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; // mushrooms // works with any index; // pepperoni; // 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

24:51 - Class static block

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