TypeScript does not infer about delete operator and spread operator?

Question

interface Test {
    a: string;
    b: number;
    c: number;
}

const test = {
    a: 'a',
    b: 1,
    d: []
};

delete test.d;

const test2:Test = { ...test, c:1 };
=> Type '{ a: string; b: number; c: number; d: never[]; }' is not assignable to type 'Test'.
=> Object literal may only specify known properties, and 'd' does not exist in type 'Test'.

I deleted d property by delete operator, but I got a error like that.

Is there a way for the situation?

Answer 1

The type of the variable is infered on assignment, and I don't think Typescript does any flow control magic with the delete operator. You could the spread operator to get rid of d:

interface Test {
    a: string;
    b: number;
    c: number;
}

const test = {
    a: 'a',
    b: 1,
    d: []
};

let { d, ...test3} = test

const test2:Test = { ...test3, c:1 };