Introduction In this blog, you are going to learn how JavaScript built-in methods work internally. You will also learn how developers make JavaScript compatible with older browsers using polyfills. What are polyfills : A polyfill is a piece of JavaScript code that adds support for modern features in older browsers that don’t support them natively. If the browser doesn’t have a feature, we create it ourselves. Example : Let's take an example that older browser doesn't support Array.prototype.includes. We write polyfill like this if ( ! Array . prototype . includes ) { Array . prototype . includes = function ( value ) { for ( let i = 0 ; i < this . length ; i ++ ) { if ( this [ i ] === value ) { return true ; } } return false ; }; } Enter fullscreen mode Exit fullscreen mode What are Built-in methods? Built-in methods are predefined functions provided by the JavaScript runtime environment that are used to perform specific tasks. We don’t need to write the logic from scratch.…