fix: Significantly improve Duration types

[zardoy]

This PR improves Duration plugin types.

Why?

• Autocomplete:

• And for more strict checks (just compare):

New types

// That's how computed type looks like
type plugin.DurationUnitsObjectType = {
    milliseconds?: number;
    seconds?: number;
    minutes?: number;
    hours?: number;
    days?: number;
    months?: number;
    years?: number;
    weeks?: number;
}

I also added CreateDurationType to reduce code duplication, so duration(), duration.add() and duration.substract() using the same function signature.
Other changes you can view in diff. Please, let me know if don't understand something. I can explain every line of code.

UPD: With this PR TypeScript users can't use functions duration(), duration.add() and duration.substract() without args any more. But I don't think it's a breaking change, because I can't find any example usage in docs for this. In this way we just get empty duration object.

P.S. It also would be good to update TypeScript in devDependencies to latest version.

[codecov]

Codecov Report

Merging #1338 (246705e) into dev (02d96ec) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               dev     #1338   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          176       176           
  Lines         1725      1725           
  Branches       394       394           
=========================================
  Hits          1725      1725           

Impacted Files	Coverage Δ
src/locale/sl.js	100.00% <0.00%> (ø)

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[iamkun]

Thanks. Will the syntax require the latest Typescript run time? Cause I can see some of our users still using very old typescript like 1.x

[zardoy]

Thank you for noticing that, but Day.js already uses Partial, that was introduced in TypeScript 2.1

dayjs/types/index.d.ts

Line 414 in fe5f1d0

export function locale(preset?: string | ILocale, object?: Partial<ILocale>, isLocal?: boolean): string

And unknown type, that was introduced in TypeScript 3.0

dayjs/types/index.d.ts

Line 412 in fe5f1d0

export function extend<T = unknown>(plugin: PluginFunc<T>, option?: T): Dayjs

But it is not a big problem because if TypeScript does not understand something it will fallback to any type.
Just compare computed variant of extend function:

// TypeScript 1.8.10 (TypeScript doesn't understand this Generic so it fallbacks to `any` type)
function extend<T, unknown>(plugin: any, option?: T): Dayjs
// TypeScript 2.9.2 (TypeScript still doesn't understand `unknown` type)
function extend<T = any>(plugin: PluginFunc<T>, option?: T): Dayjs
// TypeScript 3.0.0 and higher
function dayjs.extend<T = unknown>(plugin: PluginFunc<T>, option?: T): Dayjs

So the answer is: It will work, but with fallbacks to any type:

type plugin.CreateDurationType = ((units: any) => Duration) & ((time: number, unit?: any) => Duration) & ((ISO_8601: string) => Duration)

And only if the user uses TypeScript 2.x all the types will work correctly.
I think it would be good to encourage users to upgrade TypeScript version. Breaking changes for all TypeScript versions could be found here: https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#typescript-20 .

[zardoy]

Don't worry intellisense will work correctly (even if the user still uses TypeScript 1.x):

[iamkun]

LGTM

[iamkun]

Thank you, TS expert.

Just wondering if you could help us with another TS issue if you got some time.

#1281

[iamkun]

🎉 This PR is included in version 1.10.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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