TypeScript：重命名一个属性的另一种类型的类型

Question

Is it possible to create a function that transform an object by renaming one property, and properly returns the type of this?

Example:

My input type:

type In = {
  foo: string;
  bar: number;
};

const in: In = {foo: 'hello', bar: 42};

I want to call a function that renames foo to convertedFoo , while maintaining its type (string), and has a return type that reflects this object.

const out = convert(in, 'foo', 'convertedFoo')

Now I want out to be {convertedFoo: 'hello', bar: 42}

I tried

function convert<T>(obj: T, oldProp: keyof T, newProp: string): Omit<T, oldProp> & {[newProp]: T[oldProp]} {
    const {[oldProp]: id, ...rest} = obj;

    return {...rest, [newProp]: id};
}

But this (obviously) doesn't work since oldProp cannot be passed to Omit dynamically, and newProp cannot be used as a computer property name in a literal.

Is this at all possible to accomplish?

Answer 1

Try this:

const in_var = {
    foo: 'hello',
    bar: 42,
    step: true
}; // in is keyword
function convert<T, OldProp extends keyof T, NewProp extends string>(obj: T, oldProp: OldProp, newProp: NewProp) {
    const {
        [oldProp]: id,
        ...rest
    } = obj;

    return {
        ...rest,
        [newProp]: id
    } as Omit<T, OldProp> & Record<NewProp, T[OldProp]>;
}
var a = convert(in_var, "foo", "foo_new").foo_new; // intellisense works! (I trust you use Visual Studio Code)

Firstly, in is invalid variable name, it's keyword. Then you cannot use {[newProp]: T[oldProp]} because you mix values and types. Better was {[x: NewProp]: T[OldProp]} but TypeScript throws an error, because it doesn't know if NewProp is string or number. Use Record. I spend one hour for answer, I trust it's correct.