What are some examples of JavaScript polyfills?

What are some examples of JavaScript polyfills?

JavaScript polyfills are scripts that provide modern functionality on older browsers. For example, the Array.prototype.includes method can be polyfilled to support browsers that don't have it natively.

Can you show me how to create a polyfill for Array.prototype.includes?

Sure! Here's a simple polyfill for Array.prototype.includes:

if (!Array.prototype.includes) {
    Array.prototype.includes = function(searchElement, fromIndex) {
        if (this == null) {
            throw new TypeError('Array.prototype.includes called on null or undefined');
        }
        const O = Object(this);
        const len = O.length >>> 0;
        if (len === 0) return false;
        let n = fromIndex | 0;
        let k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);
        while (k < len) {
            if (O[k] === searchElement) return true;
            k++;
        }
        return false;
    };
}

What other polyfills are commonly used?

Other commonly used polyfills include:

1. Promise for asynchronous programming.
2. fetch for making network requests.
3. Object.assign for merging objects.

How do I know if I need a polyfill?

You might need a polyfill if you're using modern JavaScript features that aren't supported in the browsers your application needs to support. Tools like Babel can help identify these.