Decorators Implementation Updates
Refresher: What is a decorator?
Decorators are functions which have four main capabilities when applied to a class or class element: Replacement, Initialization, Metadata, and Access
Common Use Cases
- Validation libraries, dynamic type systems
- ORMs, declarative data structures and models
- Reactivity libraries
- Method binding
- Debugging tools
- Dependency injection
Refresher: Why classes, and why at all?
// Decorator pattern without syntax
// Option 1
class C {
// - New memoized function created
// for every instance, overhead
memoizedMethod = memoize(() => {
// ...
});
}
// Option 2
class C {
memoizedMethod() {}
static {
// - Imperative
// - Can be conditional, more complex
// - Can't be typed easily
// - Difficult to understand
C.prototype.memoizedMethod =
memoize(C.prototype.memoizedMethod);
}
}// Decorator pattern without syntax
function memoize(fn) {
return (...args) => {
// ...impl
}
}
// + Concise, declarative, easy
// to understand
// + Performant, only one
// decorated function exists
const memoizedFunc = memoize(() => {
// ...impl
});Community interest remains high
Number 2 most exciting feature in State of JS 2024 Survey
Current Implementation Status
- Transforms have been shipped in TypeScript and Babel, and have been widely adopted by the community
- Tests have been written for Test262 (not yet merged due to time constraints for the champion, but comprehensive: PR)
- Edge is nearing completion in V8
- SpiderMonkey is around 75% complete
- Additional proposals which build on Decorators are currently in a holding pattern until it is complete:
- Parameter decorators
- Function decorators
- Grouped and auto accessors
Implementer feedback
- Several implementers have expressed some hesitation in being the first to ship decorators.
- We'd like to take some time to discuss those concerns in plenary.
Decorators Implementation Updates
By pzuraq
