30-seconds-of-code/snippets/leftSubstrGenerator.md

title, tags, expertise, cover, author, firstSeen

title	tags	expertise	cover	author	firstSeen
Left substring generator	string,generator	intermediate	blog_images/boutique-home-office-1.jpg	chalarangelo	2022-07-24T05:00:00-04:00

Generates all left substrings of a given string.

• Use String.prototype.length to terminate early if the string is empty.
• Use a for...in loop and String.prototype.slice() to yield each substring of the given string, starting at the beginning.

const leftSubstrGenerator = function* (str) {
  if (!str.length) return;
  for (let i in str) yield str.slice(0, i + 1);
};

[...leftSubstrGenerator('hello')];
// [ 'h', 'he', 'hel', 'hell', 'hello' ]