[Feature request] allow use `as const` + `type` or `interface`

Search Terms

Suggestion

Use Cases

allow use as const + type or interface

so we can make sure as const is follow type or interface

Examples

check as const output is follow IVueCliPrompt[]

.ts

interface IVueCliPrompt
{
	name: string,
	type: 'confirm' | string,
	message: string,
	default: unknown
}

const prompts = [
	{
		name: 'replaceFiles',
		type: 'confirm',
		message: 'Replace current files with preset files?',
		default: false
	},
] as const IVueCliPrompt[];

export = prompts

.d.ts

declare const prompts: readonly [{
    readonly name: "replaceFiles";
    readonly type: "confirm";
    readonly message: "Replace current files with preset files?";
    readonly default: false;
}];
export = prompts;

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, etc.)
• This feature would agree with the rest of TypeScript’s Design Goals.

[greg-hornby-roam]

I believe he wants to use the as const feature while still type checking that the structure matches an interface. A workaround I’d use for something like that would be

interface ITest {
  a: number;
  b: string;
}

let foo = {
  a: 5,
  b: "Hello"
} as const;

<ITest>foo; //a useless javascript line, but checks the var `foo` is assignable to `ITest`

[AnyhowStep]

This StackOverflow question can be solved with this, https://stackoverflow.com/questions/57069802/as-const-is-ignored-when-there-is-a-type-definition