All primitives can be spread in objects according to MDN but TypeScript prevents it about typescript HOT 11 OPEN

The inferred type of someCondition is string | null:

Are you absolutely sure? Because then it should work. That it does work when you use a type assertion indicates the type is not as you think it is.

from typescript.

For null and undefined it's intentional: #57501. I suspect for the other types as well. Spreading them makes no sense and indicates a logic error.

from typescript.

What JavaScript allows at runtime and what TS allows at compile time are intentionally very different things.

Since these are no-ops, there's no reason to ever write e.g. { ...true } literally instead of just {}. And if you have something like boolean | Foo where it's only sometimes an object that you're spreading in, then that's likely to indicate a bug in your code, so TS errors accordingly.

from typescript.

Related #38469

from typescript.

Thanks for the quick feedback.

The use case is this (we have a lot of instances of it in the codebase at my current company):

const someObject = {
  someProperty,
  ...(someCondition && { someConditionalProperty })
};

It is perfectly valid in JavaScript but in TypeScript we have to write this instead, which is a little awkward:

const someObject = {
  someProperty,
  ...(someCondition ? { someConditionalProperty } : {})
};

from typescript.

This checks without error:

declare const someProperty: { x: string };
declare const someCondition: boolean;
declare const someConditionalProperty: { y: string };
const someObject = {
  someProperty,
  ...(someCondition && { someConditionalProperty })
};

What are your actual types?

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The inferred type of someCondition is string | null:

import { useSelector } from 'react-redux';

const someCondition = useSelector(state => state.someCondition);

What is weird is that the spread does type check without error if I use a type assertion:

import { useSelector } from 'react-redux';

const someCondition = useSelector(state => state.someCondition) as string | null;

from typescript.

You seem to be reducing these examples so far that they stop working or making sense. I'd really like an actual example of this problem occurring to make sure nothing weird is happening.

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