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Decorators · Issue #2249 · microsoft/TypeScript · GitHub
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CommittedThe team has roadmapped this issueThe team has roadmapped this issueES NextNew featurers for ECMAScript (a.k.a. ESNext)New featurers for ECMAScript (a.k.a. ESNext)FixedA PR has been merged for this issueA PR has been merged for this issueSuggestionAn idea for TypeScriptAn idea for TypeScript
Description
ES7 proposal
The ES7 proposal for decorators can be found here: https://github.com/wycats/javascript-decorators
The ES7 proposal serves as the base of this proposal. Below are notes about how the type system
Decorator targets:
Class constructor
@F("color")
@G
class Foo {
}
desugars to:
var Foo = (function () {
function Foo() {
}
Foo = __decorate([F("color"), G], Foo);
return Foo;
})();
Methods
class Foo {
@F(color)
@G
bar() { }
}
desugars to:
var Foo = (function () {
function Foo() {
}
Foo.prototype.bar = function () {
};
Object.defineProperty(Foo.prototype, "bar", __decorate([F(color), G], Foo.prototype, "bar", Object.getOwnPropertyDescriptor(Foo.prototype, "bar")));
return Foo;
})();
Static method
class Foo {
@F("color")
@G
static sMethod() {}
}
desugars to:
var Foo = (function () {
function Foo() {
}
Foo.sMethod = function () {
};
Object.defineProperty(Foo, "sMethod", __decorate([F("color"), G], Foo, "sMethod", Object.getOwnPropertyDescriptor(Foo, "sMethod")));
return Foo;
})();
Properties
class Foo {
@F("color")
@G
prop: number;
}
desugars to:
var Foo = (function () {
function Foo() {
}
__decorate([F("color"), G], Foo.prototype, "prop");
return Foo;
})();
Method/Accessor formal parameter
class Foo {
method(@G a, @F("color") b) {}
}
desugars to:
var Foo = (function () {
function Foo() {
}
Foo.prototype.method = function (a, b) {
};
__decorate([G], Foo.prototype, "method", 0);
__decorate([F("color")], Foo.prototype, "method", 1);
return Foo;
})();
Where the __decorate is defined as:
var __decorate = this.__decorate || function (decorators, target, key, value) {
var kind = typeof (arguments.length == 2 ? value = target : value);
for (var i = decorators.length - 1; i >= 0; --i) {
var decorator = decorators[i];
switch (kind) {
case "function": value = decorator(value) || value; break;
case "number": decorator(target, key, value); break;
case "undefined": decorator(target, key); break;
case "object": value = decorator(target, key, value) || value; break;
}
}
return value;
};
Decorator signatures:
A valid decorator should be:
- Assignable to one of the Decorator types (ClassDecorator | PropertyDecorator | MethodDecorator | ParameterDecorator) as described below.
- Return a value (in the case of class decorators and method decorator) that is assignable to the decorated value.
declare type ClassDecorator = <TFunction extends Function>(target: TFunction) => TFunction | void;
declare type PropertyDecorator = (target: Object, propertyKey: string | symbol) => void;
declare type MethodDecorator = <T>(target: Object, propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<T>) => TypedPropertyDescriptor<T> | void;
declare type ParameterDecorator = (target: Function, propertyKey: string | symbol, parameterIndex: number) => void;
Notes:
- Decorating a function declaration is not allowed as it will block hoisting the function to the top of the scope, which is a significant change in semantics.
- Decorating function expressions and arrow functions are not supported. The same effect can be achived by applying the decorator function as
var x = dec(function () { });
- Decorating function formal parameters is currently not part of the ES7 proposal.
- Decorators are not allowed when targeting ES3
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CommittedThe team has roadmapped this issueThe team has roadmapped this issueES NextNew featurers for ECMAScript (a.k.a. ESNext)New featurers for ECMAScript (a.k.a. ESNext)FixedA PR has been merged for this issueA PR has been merged for this issueSuggestionAn idea for TypeScriptAn idea for TypeScript
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