In the previous chapter, we exported and imported a module in a .ts file. Although, using ES Modules without making the required configuration changes will result in the error "SyntaxError: Cannot use import statement outside a module". You do not need to be using, or even be a fan of, Angular 2 or Typescript for them to be useful for you. If the TypeScript code uses a feature that is not supported by the targeted version, then it is compiled to equivalent code that only uses supported features. This file contains a unit test for index.ts: As you can see, we are running the compiled version of the test (in directory dist/), not the TypeScript code. This means you would have to either NOT use ECMA 6 at all in your components Angular 2 references, or have two versions of your library, one using ECMA 5 and one using ECMA 6. Because we are just using PlaywrightTestConfig as a type, an easy fix for this issue is to import it as a type: Just by adding type after import tells TS this should not be added to the output file. It then just resolves the type for type checking and the error is resolved. The portion of the gulpfile.js of interest is as follows: The item of interest for now is module: commonjs. We cannot use TypeScript modules directly in our application. When running our unit tests, we get the following error: The problem arise because jest is trying to get the jest.config.js file using Nodejs resolver. If youre interested in the details of that module support then its worth reading this post on ECMAScript modules. For example, the script clean is invoked via npm run clean. As we do this, well discuss what it looks like to author ECMAScript modules for Node.js in TypeScript. How to change a package from commonjs to module. What is new is the official TS support of these features. When trying to run it, we get the following error: This happens because of how playwright/test exposes its types.
To make this easy to work with, we define two core folders as follows: Internal modules in Typescript allow you to structure your pre ECMA 6 modules code into separate files and then have Typescript combine all the files together (similar to bundling via Browserify and Webpack) and provide a level of namespacing away from the global scope. Additionally, Babel can be used for TypeScript compilation, and the TypeScript compiler will be used for type checking, as Babel can not type check TypeScript code. Although it is important to note that the file imported must end with a ".js" file extension rather than a ".ts" file extension. The previous package.json contains the following scripts: clean uses the cross-platform package shx to delete the compilation results via its implementation of the Unix shell command rm. npm packages directories with files that are installed via the npm package manager. Do not use TypeScript internal modules, delete them from your code, forget they exist, and move to TypeScript external modules. There are a few more differences between module and commonjs and you can read about them in the nodejs documentation. When developing an npm package, there are many considerations one needs to take regarding consumption. When type value is commonjs (or not specified), files expected to be consumed by the commonJS way (require). Thats why Lodash is a normal dependency it is needed at runtime. The change is seemingly simple. While developing our design system ui components Vivid, we gained a lot of knowledge and experience regarding types of consumers. To get the JavaScript files for the TypeScript modules, we need to compile modules using TypeScript compiler. If the nearest parent package.json lacks a type field, or contains type: commonjs, .js files are treated as CommonJS. In regards to performance, with ESM import you can selectively load only the pieces you need. Now you can use this configuration to create node modules that are statically typed and run in Node.js using the ES Module format. You can see the commit here. Before we close out, it might be interesting to look at what TypeScript is doing when we run our npm run build.
I have 15 years of experience building Enterprise applications before launching my own product ag-Grid Enterprise. MacGyver turned Dev TypeScript / ts-loader / fork-ts-checker-webpack-plugin / DefinitelyTyped: The Movie, This can be set to either module or commonjs, to optimize your application's performance, Test and debug Android apps like a pro with Charles Web Proxy, Using React Native ScrollView to create a sticky header, Fleet: A build tool for improving Rusts Cargo, There was already an established module system used in Node.js called, Node.js itself did not initially offer support for ECMAScript modules; in large part because of the problems associated with being able to support CommonJS. Well also update the "scripts" section of our package.json to include build and start scripts: With all that set up, were ready to write some TypeScript ECMAScript modules. (I deliberately have not published it as a package to npm.). When we did that, it worked as follows: In module mode, TS will throw an error for files without a extension so you will have to import like this: import { cleanup } from '../utils/helpers.js'; You can also exempt files from this behavior by using special extensions. This is where Babel is configured to use ES Modules as the "modules" setting is set to false, which is somewhat confusing because ES Modules are being used. It is also recommended, when using TypeScript with the Babel compiler, to set the "allowSyntheticDefaultImports" and "isolatedModules" to true as this ensures that the TypeScript compiler will process source code similar to how the Babel compiler does. Since the JavaScript code is being output to a folder named "dist" the "main" property in the package.json should be changed to: To run the compiled JavaScript code, execute the command npm run start and this will carry out the type checking and compilation steps as well as run the index.js file with Node.js. Back then it was known as ES6 modules. This informs the TypeScript compiler to recognize source code in the ES Module format as well as retain the format when generating JavaScript code. Without the former, we cant use the latter. The ultimate solution to this is to use fileFromUrl(new URL('.
Do not do any of this!! ag-Grid uses Gulp for compiling TypeScript and has the TypeScript settings in the Gulp file. We will tweak the module option to be nodenext to opt into ECMAScript module support: Weve also set the outDir option, such that compiled JavaScript will go into that directory, and the declaration option such that .d.ts files will be generated. It is standard practice to put these main files in the root of your project. This is what we think about them: ag-Grid uses Gulp to configure TypeScript. To use the "clean" and "compile" script sequentially they are combined in a new script named "build", which can be run using the command npm run build. In this example there are two extra babel settings included that instruct the Babel compiler to remove any comments in the source code and minify the JavaScript output. When ES6 shipped back in 2015, with it came the concept of modules for JavaScript. Using ES Modules does not require the use of TypeScript, however the overhead of including TypeScript is minimal and including it provides many benefits such as static typing, which can enable code editors or an IDE to offer more predictive assistance. Happily, Node.js allows ES modules to import CommonJS modules as if they were ES modules with a default export; which is good news for interop. Additionally the compilation target is set to Node so that Babel can apply code transforms that ensure the code will be able to run in the LTS version of Node.js. The command that will be most commonly used is the "build-typecheck" command, which can be used by running npm run build-typecheck. Understanding Unit Tests in Javascript: 5 Frameworks, Typescript changes the import depending on your.
ESM modules has been with us for a while now. Are these normal dependencies or dev dependencies? Were going to make a module named greeter lets initialize it: We now have a package.json that looks something like this: Node.js supports a new setting in package.json called type. With TypeScript configured, we can add the Babel configuration that enables TypeScript compilation with the Babel compiler. This will install the npm packages in the project "node_modules" folder and create a package-lock.json file. Heres the commit for this one. Why use ECMAScript modules (import) instead of CommonJS (require)? Supporting all the frameworks and build systems took days of research and practicing. Historically, we had only the main property. Theres a number of reasons for this: However, with the release Node.js 14 support for ECMAScript modules (also known as ESM) landed. Note that when we are using an IDE, we dont need the scripts build and watch because we can let the IDE build the artifacts. Now when we run our tests, we stumble into a new difference between module and commonjs: __dirname does not exist when you use type: module. CommonJS modules a module format that originated in, and was designed for, server-side JavaScript. If you are writing your project for distribution in TypeScript, then you dont need to put your definitions in Definitely Typed. Although, before doing so make sure to have Node.js and npm installed. At this point the source code is configured to run with ES Modules, so we can now look at how to compile the code and run it with Node.js. We are AG Grid and our mission is to build the best datagrid in the world. See the ag-Grid project for the full working version. This means if you included these dependencies in your project they would be dragged into your bundled files. In this chapter, we are using what TypeScript currently supports best: Especially on Node.js, TypeScript currently doesnt really support ECMAScript modules and filename extensions other than .js. Recently, typescript (TS) announced the nodenext module support from version 4.7.x. First well write a greetings.ts module: There is nothing new or surprising about this; its just a module exporting a single function named helloWorld. Otherwise, the package is only needed during development time and a dev dependency.
It takes a CommonJS module and generates a bundle that exposes the shared component on the global namespace. Then in the "src" folder create a new file named "helpers.ts" and place the following code in it: This code is only logging the value that is passed in to the console, and is not really representative of actual code that would be used, but it allows for the demonstration of using ES Modules with TypeScript and Babel. Now lets try to run our ui-tests (we use playwright).