Better typings for KeyboardEvent.key

[iway1]

KeyboardEvent.key is typed as a string, even though it's a union of string literals.

window.addEventListener('keydown', (e)=>{
  // string type
  e.key
})

Would be really nice to get autocomplete here =D

[qb20nh]

https://www.w3.org/TR/uievents-key/#keys-unicode

Almost every Unicode character can be used as a valid key attribute value, but there is a small set of Unicode characters which MUST NOT be used. We introduce the concept of a key string to identify the set of Unicode strings that are appropriate for use as a key attribute value.

A key string is a string containing a 0 or 1 non-control characters ("base" characters) followed by 0 or more combining characters. The string MUST be in Normalized Form C (NFC) as described in [UAX15].

A non-control character is any valid Unicode character except those that are part of the "Other, Control" ("Cc") General Category.

A combining character is any valid Unicode character in the "Mark, Spacing Combining" ("Mc") General Category or with a non-zero Combining Class.

Listing all possible value is possible but impractical considering all the keyboard configurations around the globe and ever changing Unicode standard. Quick good enough solution could be only including US keyboard keys plus predefined keys.

[tommy-mitchell]

Related: microsoft/TypeScript#38886

[qb20nh]

Hack to make autocompletion work: microsoft/TypeScript#29729 (comment)

type LiteralUnion<T extends U, U = string> = T | (U & { zz_IGNORE_ME?: never })

type Color = LiteralUnion<'red' | 'black'>

var c: Color = 'red'                    // Has intellisense
var d: Color = 'any-string'             // Any string is OK
var d: Color = { zz_IGNORE_ME: '' }     // { zz_IGNORE_ME } placeholder is at the bottom of intellisense list and errors because of never 

type N = LiteralUnion<1 | 2, number> // Works with numbers too