Distributive as const

Search Terms

as const, widening, literal widening

Suggestion

Allow to use as const on ternary operator as well as others code branches that currently we can't.

Use Cases

Let's say that we have this code:

const result = (
  value > 5
    ? { amount: 'many' } as const
    : { amount: 'few' } as const
)

We need to type as const twice. So would be nice if we could type just once:

const result = (
  value > 5
    ? { amount: 'many' }
    : { amount: 'few' }
) as const

Currently we can't do that (playground).
It's just a syntax sugar. It won't change anything on as const!

Analogously, maybe we could allow this syntax sugar on function:

const func = (param: number) => {
  if (param > 5) {
    return 'many' as const
  }

  return 'few' as const
}

// would be just...
const func = (param: number): const => {
  if (param > 5) {
    return 'many'
  }

  return 'few'
}

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.

Start with the linked TypeScript Playground example to reproduce the rejected as const placement and compare it with the accepted branch-level form. No source files or tests are named; identify the compiler and test entry points for const assertions, then verify that the proposed ternary syntax is accepted without changing emitted JavaScript or existing behavior.