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
dflag 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
inkeyword
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
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
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