---
title: Left substring generator
type: snippet
language: javascript
tags: [string,generator]
cover: boutique-home-office-1
author: chalarangelo
dateModified: 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.

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

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