typescript string split with remainder

split.test.ts

import { split } from './utils';

test('string split', () => {
  const p = split("a b c d", " ", 2);
  expect(p).toStrictEqual(["a", "b c d"]);
});

test('string split nonexistent', () => {
  const p = split("a b c d", ",", 2);
  expect(p).toStrictEqual(["a b c d"]);
});

test('string split under max', () => {
  const p = split("a b c d", " ", 10);
  expect(p).toStrictEqual(["a", "b",  "c",  "d"]);
});

test('string split at max', () => {
  const p = split("a b c d", " ", 4);
  expect(p).toStrictEqual(["a", "b",  "c",  "d"]);
});

test('string split with trailing', () => {
  const p = split("a b c d ", " ", 2);
  expect(p).toStrictEqual(["a", "b c d "]);
});

test('string split with trailing at max', () => {
  const p = split("a b c d ", " ", 4);
  expect(p).toStrictEqual(["a", "b",  "c",  "d "]);
});

test('string split with trailing beyond max', () => {
  const p = split("a b c d ", " ", 10);
  expect(p).toStrictEqual(["a", "b",  "c",  "d"]);
});


test('string split with removed redundant separators', () => {
  const p = split("a  b   c d ", " ", 5);
  expect(p).toStrictEqual(["a", "b",  "c",  "d"]);
});

test('string split with removed redundant separators', () => {
  const p = split("a  b   c d ", " ", 10);
  expect(p).toStrictEqual(["a", "b",  "c",  "d"]);
});

test('string split with removed redundant separators 2', () => {
  const p = split("a   b   c  d  ", " ", 4);
  expect(p).toStrictEqual(["a", "b",  "c",  "d  "]);
});

split.ts

// string split that preserves the remainder

export function split(str: string, separator: string, limit: number): string[] {
    const result: string[] = [];
    let lastIndex = 0;
    let count = 0;

    while (count < limit - 1) {
        const index = str.indexOf(separator, lastIndex);
        if (index === -1) break;
        const substr = str.slice(lastIndex, index);
        if (substr !== "") {
            result.push(substr);
            count++;
        }
        lastIndex = index + separator.length;
    }

    // trim any leading separators from the last element
    const remaining = str.slice(lastIndex).replace(new RegExp("^"+separator+"+", "i"), "");
    if (remaining !== "") {
        result.push(remaining);
    }

    return result;
}