Improvement: Design metadata should contain property names and types

[Cedware]

At the moment it's not possible to get all Properties of a Type with the corresponding design-type of the property.
It's only possible to get all properties of an object by using Object.keys() and this wouldn't return properties which haven't been set, of course the simply don't exist.
So it wold be a great feature, if a class which emits metadata because of a decorator would also emit a metadata called something like 'design:properties' which contains a list of all property-names with the corresponding type.

[mhegazy]

Can you elaborate on the scenario you are trying to achieve?

[Cedware]

Alright lets take a look at this simple class:

export class MyClass{
    public stringProperty: string;
    public numProperty: number;
    constructor(stringParam: string){
    }
}

with --emitDecoratorMetadata the following code is emitted:

var MyClass = (function () {
    function MyClass(stringParam) {
    }
    MyClass = __decorate([
        my_decorator_1.myDecorator, 
        __metadata('design:paramtypes', [String])
    ], MyClass);
    return MyClass;
}());

I think it would be useful, if the emitted js would contain additional metadata which describes the designtime properties of the class:

var MyClass = (function () {
    function MyClass(stringParam) {
    }
    MyClass = __decorate([
        my_decorator_1.myDecorator, 
        __metadata('design:paramtypes', [String])
        __metadata('design:properties', [
        {name: 'stringProperty', type: String, visibility: 'public'},
        {name: 'numProperty', type: Number, visibility: 'public'}
        ])
    ], MyClass);
    return MyClass;
}());

So Reflect.getMetadata can be used to get all properties of a type in the same way it can be used to get all parameters of the constructor:

let constructorParams = Reflect.getMetadata('design:paramtypes', MyClass);
let propeties = Reflect.getMetadata('design:properties', MyClass);

I hope this makes the scenario more understandable

[leviathanbadger]

For what it's worth, I agree with this feature request entirely. The exact format of the properties and the name of the metadata decorator are up for interpretation, but the feature itself needs to be here in some form.

A question that comes to mind (not a problem): should we store "readonly" and other type modifiers in this way?

[aluanhaddad]

With the recent decision to emit assignments of undefined for class property declarations without an initializer this might make more sense than it once did. This might have to be under an additional flag as the size of the emit would increase dramatically.

@aboveyou00 I don't think serializing private, public, or readonly would make sense at this point. Certainly not until the private fields proposal works its way further through TC39.

[listepo-alterpost]

Hi, any news?

[IonelLupu]

There has been almost one year. Are there any updates on this? @Cedware @mhegazy

Hey guys, any updates on this? thx

[IRCraziestTaxi]

This is exactly what I need! What's the status on this?

Also, @aluanhaddad, what do you mean by "the recent decision to emit assignments of undefined for class property declarations without an initializer"? That sounds very promising for what I'm trying to do, but I'm not sure what you're referencing and google with those and similar search terms doesn't turn up anything for me.

[nodkz]

Is there a way to make USE_NEW_TYPE_METADATA_FORMAT=true for
https://github.com/Microsoft/TypeScript/blob/90b304aa5e93a8195e4b8bcfb65b0079391cb9cf/src/compiler/transformers/ts.ts#L1659-L1661

It will unlock desired behavior
https://github.com/Microsoft/TypeScript/blob/90b304aa5e93a8195e4b8bcfb65b0079391cb9cf/src/compiler/transformers/ts.ts#L1681-L1697

[nodkz]

This feature was reverted in #7878 by @rbuckton

@mhegazy said on Apr 7, 2016

As discussed offline, we should limit the breaking change for this iteration, and include these changes later on.

But what about just adding design:typeinfo to the old method addOldTypeMetadata without breaking changes?
https://github.com/Microsoft/TypeScript/blob/90b304aa5e93a8195e4b8bcfb65b0079391cb9cf/src/compiler/transformers/ts.ts#L1693-L1695

[IonelLupu]

@nodkz is this really possible? I am hunting these new features of TS that are about to be introduced. for one of my projects.

These features will make Typescript become a next level language. I think we need to add a flag or something to ts that opens a new set of features like this.