Refactoring to add inferred return type annotation to a function

[mjbvz]

Search Terms

• Refactoring, refactor
• type annotation
• quick fix, code action
• function, method
• return

Suggestion

Add a refactoring that takes a function with no annotated return type, and inserts the inferred return type.

For example, starting with the code:

function foo() {
  return { a: 1, b: 2 };
}

If you trigger the refactoring on foo, it would become:

function foo(): { a: number; b: number; } {
  return { a: 1, b: 2 };
}

Use Cases

A few example use cases:

• Give your public interfaces explicit typings.

• Updating a function from () => T to () => T | undefined. Today, you have to explicitly type out the return type and then add | undefined

• Extracting the return type to a new interface. Right now, this is a manual process. With this refactoring, this becomes a two step process: generate inferred return type and then extract to interface

• When migrating from JS to TS, many JS functions may not have explicit return types. Often you want to make the code stricter by having these return types

[jsamr]

Isn't it similar to #35467? But agree, would be extremely useful.

[mjbvz]

Yes but this one is more generic. You can can think of #35467 as a one step version of one refactoring this request would enable as two steps: add types, then extract type.