Suggestion: extract to function expression

Search Terms

function expression declaration extract method refactoring code fixes

Suggestion

"Extract to function" is very useful, but it only supports generating function declarations. Some people (such as me) prefer to use function expressions instead of declarations.

For example:

const fn = () => {
    const foo = 1;
    const bar = foo + 2
}

If I select line 3 and extract to function, I get

const fn = () => {
    const foo = 1;
    const bar = newFunction(foo)
}

function newFunction(foo: number) {
    return foo + 2;
}

I want:

const newFunction = (foo: number) => foo + 2;

const fn = () => {
    const foo = 1;
    const bar = newFunction(foo)
}

Some ideas:

• An option to toggle between expressions/declarations
• Separate refactorings for both expressions and declarations

Use Cases

Examples

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.

No files or tests are named in the issue; start by locating the existing “Extract to function” refactoring entry point and its tests. Compare the requested function-expression output with current declaration behavior, then determine whether a toggle or separate refactoring is the intended completion criterion and cover both TypeScript and JavaScript cases.