A robust & optimized polyfill for the String.prototype.startsWith method in ECMAScript 6.

This package implements the es-shim API interface. It works in an ES3-supported environment and complies with the spec.

Other polyfills for String.prototype.startsWith are available:

• https://github.com/paulmillr/es6-shim/blob/d8c4ec246a15e7df55da60b7f9b745af84ca9021/es6-shim.js#L166-L173 by Paul Miller (fails some tests: 1, 2 passes all tests)
• https://github.com/google/traceur-compiler/blob/315bdad05d41de46d25337422d66686d63100d7a/src/runtime/polyfills/String.js#L19-L37 by Google (fails a lot of tests now uses this polyfill and passes all tests)

Via npm:

npm install string.prototype.startswith

Then, in Node.js:

var startsWith = require('string.prototype.startswith');

In a browser:

<script src="https://bundle.run/string.prototype.startswith"></script>

NOTE: It's recommended that you install this module using a package manager such as npm, because loading multiple polyfills from a CDN (such as bundle.run) will lead to duplicated code.

Polyfills + test suites for String.prototype.endsWith and String.prototype.contains are available, too.

1. On the main branch, bump the version number in package.json:

   npm version patch

   Instead of patch, use minor or major as needed.

   Note that this produces a Git commit + tag.

2. Push the release commit and tag:

   git push && git push --tags

   Our CI then automatically publishes the new release to npm.

Mathias Bynens

This polyfill is available under the MIT license.