JS Fundamentals - Decorators

In this Hasty Treat, Scott and Wes talk about whether decorators are finally here, what the uses cases are for decorators, how to define a decorator, and what auto accessor is.

Show Notes

• 00:25 Welcome
• 01:00 Are decorators finally here?
• TC39 proposal
• How this compares to other versions of decorators
• 06:47 What are use cases for decorators?
• 10:55 How do you define a decorator?
• 14:20 Auto Accessor

on classes

@loggged class C {} 

on fields

class C { @logged x = 1; } 

Auto Accessor

class C {   accessor x = 1; } 

sugar for below

class C {   #x = 1; // # means private    get x() {     return this.#x;   }    set x(val) {     this.#x = val;   } } 

Can be decorated and decorator can return new get and set and init functions

function logged(value, { kind, name }) {   if (kind === "accessor") {     let { get, set } = value;      return {       get() {         console.log(`getting ${name}`);          return get.call(this);       },        set(val) {         console.log(`setting ${name} to ${val}`);          return set.call(this, val);       },        init(initialValue) {         console.log(`initializing ${name} with value ${initialValue}`);         return initialValue;       }     };   }    // ... } 

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