Exploring Decorators in TypeScript and ECMAScript

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; } }; } // ... } Tweet us your tasty treats

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