Declare local variable as optional

[tinganho]

Every time I type an undefinable variable, I think I typed something wrong:

let a: string | undefined;

Why do I think I did something wrong? It's because I never add undefined type to a union type as above except in variable declarations.

Don't you think it is time, introduce the optional operator to local variable declarations as well?

let a?: string;

The above syntax feel very natural and idiomatic typescript for me.

[lucabrunox]

Or nullable local variables with strictNullChecks enabled.

[mhegazy]

Or nullable local variables with strictNullChecks enabled.

let a: string | null;

? never includes null. ? means "optional" for parameters and properties, meaning T | undefined.

[rwyborn]

This is absolutely needed. Maintaining code that deals with a lot of optional params/members is painful to jump back and forth between ? and type | undefined when in reality you are dealing with the exact same objects in both cases (just sometimes as params/members, and other times as locals).

I suspect people aren't bashing down the walls on this one because strictNullChecks usage isn't as common as it should be.

C# is a good example where the nullable ? modifier is equally applicable to params, locals and members.

[fwd079]

Every time I type an undefinable variable, I think I typed something wrong:

let a: string | undefined;

Why do I think I did something wrong? It's because I never add undefined type to a union type as above except in variable declarations.

Don't you think it is time, introduce the optional operator to local variable declarations as well?

let a?: string;

The above syntax feel very natural and idiomatic typescript for me.

I just tried using let s? : string = null; and failed miserably. lol

Guess till it is done let s: string | null; has to suffice. But voting for let s? : string = null; please.

Regards.

[StragaSevera]

I fully agree. Please, please, give us terser syntax for the T | null!

[adevine]

While this is an old issue I just thought I'd leave a note here in case anyone else finds this. A lot of libraries make this optional syntax nicer using generics. For example, defining Maybe as

type Maybe<T> = T | null;

which then lets you do things like let foo: Maybe<string> = null; It's not really saving on characters but I think it reads nicer. Could also do something like

type Nullish<T> = T | null | undefined;

and

type Opt<T> = T | undefined;

[zolomatok]

Has this gone anywhere?

[RyanCavanaugh]

I don't think we're likely to implement this. It's outside the defined grammar for the types-as-comments proposal and it's very confusing, semantically speaking - the variable is absolutely there, just maybe not initialized, whereas an optional property might very well be truly missing.