Improve typings for String.split #42330
Description
lib Update Request
Configuration Check
My compilation target is ES2015 and my lib is ["dom", "es2019"].
I have noUncheckedIndexedAccess set to true
Missing / Incorrect Definition
String.split
Sample Code
const parts = "a b c".split(" ");
console.log(parts[0].toUpperCase()); // Type error: parts[0] is possibly undefinedDocumentation Link
https://tc39.es/ecma262/#sec-string.prototype.split
Description
String.split returns string[]. A return type of [string, ...string[]] would be more useful when noUncheckedIndexedAccess is enabled, sinceString.split will return an array with at least one element in the vast majority of cases.
I'm not completely sure about all of the edge cases here, but as far as I can see there are two cases in which an empty array could be returned:
"".split(""), which returns[].- Using a splitter function
Given just these two edge cases, it should be pretty straightforward to return [string, ...string[]] when string | RegExp is used as separator:
// lib.es5:
split(separator: "", limit?: number): string[];
split(separator: string | RegExp, limit?: number): [string, ...string[]];
// lib.es2015:
split(splitter: { [Symbol.split](string: string, limit?: number): string[]; }, limit?: number): string[];I completely understand if you feel like this relies too much on implementation details etc, but I at least wanted to raise the issue because this is annoying me a lot!