![]() ![]() To load a script with ESM, you need to add type="module" in the script tag. For about over 95% of users ( Caniuse), ESM is supported without polyfills. The simplest way to use ESM on the web is by utilizing the native support for it. With these tips, you should not have much trouble at all converting CommonJS code to ES Modules. For example, // CommonJS const module = boolean ? require ( "module1" ) : require ( "module2" ) // ES Modules const module = await (boolean ? import ( "module1" ) : import ( "module2" ) ) If you are using Node.js v14.8 or later, you can use top-level await to make import() synchronous. Luckily, there is a simple solution to this. You can use dynamic importing to replace running require() dynamically, but problems arise with that due to how import() is asynchronous and require() is not. This snippet uses, which is available in all ESM contexts.Īnother thing that is harder to migrate is conditional imports. A simple way to polyfill _dirname is to do this: const _dirname = new URL ( ".", import. _dirname is not part of Node.js, but it is one thing that Node does not suppport in “ESM mode”. However, there are some things that are not transformed. One of the most popular tools is cjstoesm, a command line tool that automatically transforms CommonJS code in Node to its ESM equivalent. There are tools to help make migrating code from CommonJS to ES Modules easy. You can write code using ES Modules and target both ESM and CJS. TypeScript is the most notable in this category. ![]() Luckily, many compilers allow you to convert ESM to CommonJS, allowing you to write a library that offers a great experience for both groups. Unfortunately, Node does not support importing ES Modules from CommonJS modules. This feature is very helpful as it allows you to use NPM packages built with CommonJS. The most basic example is this: // script.js import The syntax used to import and export modules is a little more complicated than in other module systems like CommonJS, but it still is fairly easy to pick up. We will talk more about how to how to do this later on. Additionally, Node v12+ supports ESM, although you have to tell it you are using ESM rather than CommonJS. Today, Chrome, Safari, and Firefox fully support ESM, so you should not have any problem running it in modern browsers. ESM aims to solve all of these issues while making one module format universal. Additionally, there are some problems with CommonJS, like its synchronous nature. That is using CommonJS, which is only supported in some bundlers and Node.js. You might be familiar with importing things using require(). ES Modules aims to solve a significant problem in JavaScript: There is no built-in way to share code between scripts. It was standardized in the ES6 ECMAScript version, which you might know for adding many syntax features. However, it is a major shift from CommonJS/AMD/UMD, and it can be hard to use if you are used to one of those module formats.ĮCMAScript Modules is a module format created as part of the ECMAScript (read: JavaScript) standard. It is supported natively in most web browsers, is very fast, and opens up new opportunities for tree shaking, among other features. ESM (or ECMAScript Modules) is a modern module format with many advantages over previous formats like CommonJS. ![]()
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