Suggestion about decorators

[weiqj]

Suggestion

Relax syntax restrictions on decorations. At least do not remove parser support for decorators on interfaces.

I wouldn't mind parser-generated warnings because those can be suppressed. But if TypeScript stops parsing decorators on interfaces and interface members I will be really disappointed.

🔍 Search Terms

decorator syntax restriction interface

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

TypeScript works great as an "intermediate programming language", which is always transpiled into other languages.

Let's keep it that way! And make sure the design meets the requirements.

I would suggest TypeScript keep decorators on interfaces and interface members.

📃 Motivating Example

I am using TypeScript to transpile to Lua. And I need decorators on interfaces.

💻 Use Cases

Why can't decorators just "decorate"? It doesn't have to be meaningfully executable at all! After all, it is what meta-programming is about.

[MartinJohns]

Why can't decorators just "decorate"?

Because that's not what they are there for. Decorators are a JavaScript feature, not a TypeScript one. JavaScript has no interfaces, so there's nothing the decorator can decorate.

A few options you have:

• Use classes instead of interfaces.
• Use comments instead of decorators.
• Fork TypeScript and implement the feature yourself.

[weiqj]

Isn't TypeScript supposed to be a superset of Javascript?

You should have some vision and bring some transcendental value to this great invention.

Currently, at least pre 5.0, decorators on interfaces can be correctly parsed with a warning.

I simply suggest you keep it that way because it won't break anything. And secondly, it will bring tremendous value beyond simple Javascript transpilation!

Why can't decorators just "decorate"?

Because that's not what they are there for. Decorators are a JavaScript feature, not a TypeScript one. JavaScript has no interfaces, so there's nothing the decorator can decorate.

A few options you have:

• Use classes instead of interfaces.
• Use comments instead of decorators.
• Fork TypeScript and implement the feature yourself.

[weiqj]

@MartinJohns,
I just checked the source code. Although I am not an expert, there is clearly a utility API canHaveIllegalDecorators.

TypeScript/src/compiler/factory/utilities.ts

Line 1130 in f2df10f

export function canHaveIllegalDecorators(node: Node): node is HasIllegalDecorators {

So apparently TypeScript has been very thoughtful about this matter. Though it appears that there had been a code change to rename "decorators" into "illegalDecorators" for some classes, which I will need to look into details later.

[RyanCavanaugh]

Duplicate #2900

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.