various typescript helper functions and utility types

this library includes many helper types and functions such as add, subtract, and substring which allow the values to be known at compile time

the noUncheckedIndexedAccess compiler flag is epic, but there's room for improvement. for example, the following issue:

if (foo.length > 2) {
    const bar: string = foo[1] //error: string | undefined not assignable to string
}

can be solved with lengthGreaterThan

import { lengthGreaterThan } from '@detachhead/ts-helpers'

if (lengthGreaterThan(foo, 2)) {
    const bar: string = foo[1] //no error, foo is casted to [string, string]
}

there's also lengthLessThan, lengthGreaterOrEqual, etc.

most of the array functions in this library keep track of the length, mostly thanks to this TupleOf utility type

this library contains a helper type and function for formatting dates using the date-fns format.

const date = formatDate(new Date(), 'dd-MM-yyyy')

assert(date === '01/01/2021') //compile error, wrong date format

you can use any date format that date-fns accepts, and the FormatDate utility type will generate a template literal type to match your desired date format.

With the exactly function you can test if types or values are an exact match to a type

const a: 1 | 2 = 1
//values (also does a runtime assertion on the values)
exactly(1 as number, a) // error as `1 | 2` is not an exact match of `number`
exactly(1 as number, a as number) // no error
exactly(1 as 1 | 2, a) // no error

// mixed
exactly<number>()(a) // error as `1 | 2` is not an exact match of `number`
exactly<number>()(a as number) // no error
exactly<1 | 2>()(a) // no error

// types
type Foo = 1 | 2
exactly<1, Foo>() // error as `1 | 2` is not an exact match of `1`
exactly<1 | 2, Foo>() // no error

The Equals type allows you to check if two types are equal at the type level

Equals<number, 1 | 2> // false
Equals<any, 10> // false
Equals<unknown, never> // false

this package is designed for typescript 4.5. you will probably have issues trying to use it with older versions, tho it will probably still work if you set skipLibCheck to true in your tsconfig.json (which isn't recommended)

• nodejs
• browser
• deno (using esm.sh - eg. import { exactly } from 'http://esm.sh/@detachhead/ts-helpers/dist/utilityFunctions/misc')