Typescript: Date constructor throws error TS2556 when using spread operator

[mahalde]

TypeScript Version: 3.2.0-dev.201xxxxx

Search Terms:
date spread operator

Code

const dateFields = [2018, 5, 14, 14, 41, 11];

const date = new Date(...dateFields);

Expected behavior:
The spread syntax is used to create a new date object without a problem.

Actual behavior:
The actual date object is created, but Typescript throws the following error:
TS2556: Expected 0-7 arguments, but got 0 or more.

Playground Link:
Example Playground

Related Issues:
None

[MartinJohns]

This is the common problem that the inferred type of dateFields is number[], and not a tuple as you expect it. If you explicitly type the variable to be a tuple containing 6 numbers then it works.

const dateFields: [number, number, number, number, number, number] = [2018, 5, 14, 14, 41, 11];

const date = new Date(...dateFields);

There are several issues regarding this open. It's the same problem with literal-types.

[mahalde]

Thanks for the fast reply. I guess this kind of fixes it for the moment.

But I am using this code in an Angular project and on the first compiling when I start the project, the error still occurs and the compiling fails. If I then save a file and in this way restart the compiler, it works.

Edit: If I try to build my project, it also fails with the given error TS2556.

[MartinJohns]

You should check what TypeScript version your Angular project is using. Angular limits the supported version of TypeScript you use - you can't just use the newest TypeScript version in an angular project. You need at least TypeScript version 3.0 for this feature.

[mahalde]

Alright, thanks for the clarification! The current stable Angular release only support a TypeScript version under 2.10.

[ststeiger]

Actually, since the relevant line in DateConstructor is
new(year: number, month: number, date?: number, hours?: number, minutes?: number, seconds?: number, ms?: number): Date;

(note: the first two arguments are non-nullable)

You need to define a type that can be anything between a 2 and 7 numbers array.
That goes like this:
type DateComponents = [number, number, number, number, number, number, number] | [number, number, number, number, number, number] | [number, number, number, number, number] | [number, number, number, number] | [number, number, number] | [number, number];

const dateFields: DateComponents = [year, month, <optional>];

or alternatively, you can extend the DateConstructor by this:

interface DateConstructor
{
    new(...args: number[]): Date; // for new Date(...[a,b, etc]), predefined-constructor requires at least two numbers, so doesn't work with spread since that could be 0 arguments...
}

which unfortunately would allow to pass null to the first two arguments, though.
You'll need to extend the DateConstructor, to add the DateComponents variable-arguments-Constructor.

interface DateConstructor
{
    new(...args: DateComponents): Date;
}

[moker-monkey]

https://stackoverflow.com/questions/55887719/how-to-use-spread-as-argument-of-function/55887905#55887905

[typescript-bot]

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.