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keshav Sandhu
keshav Sandhu

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Learn polyfill in Javascript

#webdev #programming #javascript #ai

Creating a polyfill involves writing code (usually JavaScript) that emulates a newer feature in older browsers or environments that don't support that feature natively.

✅ What is a Polyfill?

A polyfill is a piece of code (usually JavaScript) that implements a modern web API or feature on browsers that do not support it.

🧱 Steps to Create a Polyfill

Let’s walk through how to create one:

1. Choose the Feature to Polyfill

Pick a feature that isn't available in all target environments. Example: Array.prototype.includes

2. Check if the Feature Exists

Use a feature detection check so the polyfill only runs when needed.

js
if (!Array.prototype.includes) {
// Provide your own implementation
}

3. Implement the Feature

Write the functionality in a way that mimics the native behavior as closely as possible.

✅ Example: Polyfill for Array.prototype.includes

js
if (!Array.prototype.includes) {
Array.prototype.includes = function(searchElement, fromIndex) {
if (this == null) {
throw new TypeError('"this" is null or not defined');
}

const o = Object(this); const len = o.length >>> 0; if (len === 0) return false; const n = fromIndex | 0; let k = Math.max(n >= 0 ? n : len - Math.abs(n), 0); while (k < len) { if (o[k] === searchElement || (typeof o[k] === 'number' && typeof searchElement === 'number' && isNaN(o[k]) && isNaN(searchElement))) { return true; } k++; } return false;
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};
}

4. Test the Polyfill

Use browsers that don’t support the feature and verify that your polyfill works correctly. You can use:

  • Old browsers (via virtual machines or BrowserStack)
  • JavaScript engines in environments like Node.js

5. Distribute or Package

  • You can include your polyfill directly in your codebase.
  • Or, publish it as an npm package for reuse.

📦 Tip: Use Existing Polyfills

Before writing your own, check:

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