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?

I think it is case, when type casting with const test2:Test = { ...test, c:1 } as Test; is acceptably. — Pavel
– Pavel, Commented Mar 31, 2018 at 19:52

Titian Cernicova-Dragomir · Accepted Answer · 2018-03-31 17:12:58Z

6

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 };

answered Mar 31, 2018 at 17:12

Titian Cernicova-Dragomir

253k37 gold badges465 silver badges395 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

left click Over a year ago

It's a good idea, except that additional variable are used. Thank you! :)

Titian Cernicova-Dragomir Over a year ago

@leftclick not ideal i know, there may be other solutions ... i can think of one with an extra function, or one that usses a type guard .. but none are perfect

Greg7000 · Accepted Answer · 2020-12-01 19:15:19Z

-1

If you are using a tsconfig.json file, consider adding:

{
  "compilerOptions": {
    ...
     "strictNullChecks": false, 
    }
    ...
}

answered Dec 1, 2020 at 19:15

Greg7000

4351 gold badge4 silver badges19 bronze badges

Collectives™ on Stack Overflow

TypeScript does not infer about delete operator and spread operator?

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related