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Home Interviews Cross-browser compatibility and polyfills In Knockout.js – MindStick
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ICSM Computer
ICSM Computer 23 Apr 2025
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Cross-browser compatibility is required when working with any Javascript framework including knochout.js, especially if you are targeting older browsers like internet explorer or specific mobile browsers. knockout is quite light in its own right and doesn't rely too much on modern browser features, but if your application uses modern JS features or apps along with knockout then it may be partially required.

It is explained here how you can handle cross-browser compatibility and polefilter in knockout.js project:

1. Knockout.js Compatibility

  • Knockout is compatible with most major browsers, including:
    • Chrome
    • Firefox
    • Safari
    • Edge
    • Internet Explorer 9+
  • For older IE versions (like IE8), additional shims/polyfills may be needed for certain features (e.g., Array.prototype.forEach, Object.defineProperty).

2. Common Polyfills You Might Need

If your Knockout app uses modern JavaScript (ES6+), you may need polyfills for the following:

Feature Polyfill
Promise core-js or Bluebird
fetch whatwg-fetch
Object.assign, Object.keys, Array.from, etc. core-js
classList (DOM element class manipulation) classlist.js
Array.prototype.includes, find, etc. core-js or manual polyfill

Example: Adding Promise and fetch polyfills

<!-- Polyfill for Promise -->
<script src="https://cdn.jsdelivr.net/npm/promise-polyfill/dist/polyfill.min.js"></script>

<!-- Polyfill for fetch -->
<script src="https://cdn.jsdelivr.net/npm/whatwg-fetch@3.6.2/dist/fetch.umd.min.js"></script>

3. Where to Load Polyfills

Load polyfills before your Knockout scripts and bindings to ensure they are available.

<head>
  <!-- Polyfills first -->
  <script src="polyfills/promise.js"></script>
  <script src="polyfills/fetch.js"></script>

  <!-- Then your libraries -->
  <script src="knockout.js"></script>
  <script src="your-app.js"></script>
</head>

4. Detecting Feature Support (Optional)

If you want to conditionally load polyfills:

if (!window.Promise) {
  var script = document.createElement('script');
  script.src = 'path/to/promise-polyfill.js';
  document.head.appendChild(script);
}

Or use libraries like Polyfill.io to automate it:

<script src="https://polyfill.io/v3/polyfill.min.js?features=default,fetch,Promise"></script>

5. Other Considerations

  • Knockout plugins may require their own polyfills.
  • When working with observableArray, avoid Array.prototype extensions that could conflict.
  • Use Babel or TypeScript with a proper target (es5) if you're compiling modern JavaScript.
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