Typescript: adding only an optional property removes type checking

Question

I'm using typescript 1.4.1 and have the following code:

var hello: {message: string};
hello = {world: 't'};

As intended, the typescript compiler outputs an error:

Type '{ world: string; }' is not assignable to type '{ message: string; }'. Property 'message' is missing in type '{ world: string; }'. (var) hello: { message: string; }

But if the type contains only an optional property such as in:

var hello: {message?: string};
hello = {world: 't'};

Then the compiler is perfectly happy, but I would like the error to be detected.

What am'I doing wrong? or is it a typescript bug?

Thanks for your help!

basarat · Accepted Answer · 2015-03-23 12:11:14Z

4

Then the compiler is perfectly happy, but I would the error to be detected. What am'I doing wrong? or is it a typescript bug?

No this is by design. extra information is okay as long as the required information (in this case nothing) is present.

answered Mar 23, 2015 at 12:11

basarat

278k60 gold badges475 silver badges528 bronze badges

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

2 Comments

Adrien Chauve Over a year ago

OK thanks, indeed! But I think this is very misleading when you have an interface full of optional properties (say HighChartsOptions for instance) and you make a typo. Typescript compiler does nothing for you in this case.

basarat Over a year ago

Here is a bit more about "why" : basarat.gitbooks.io/typescript/content/docs/why-typescript.html

Collectives™ on Stack Overflow

Typescript: adding only an optional property removes type checking

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related