For example, the name/greet example can be recast with the introduction of the export and import statements. The promise of code that runs unmodified in both environments never quite panned out because of all the ad hoc tooling needed to retrofit a module system onto the browser. This system works well enough for code restricted to server environments, but quickly runs into trouble on the browser. A module can export one or more designated objects for use in other files.įor example, a CommonJS module declares what to export by making assignments to its module object: // name.js var name = 'foo' Īnd a module consumes another module's export by invoking its require function: // greet.js var name = require( './name.js') The one adopted by Node.js, CommonJS, treats each file as an independent module with its own scope. This situation made it very difficult develop and integrate independent software packages.Ī number of solutions to this problem sprang up. For most of its existence, the only compositional tool was the order in which tags appeared in the parent HTML document. A browser's JavaScript runtime dumps all variables into the global scope by default. Most programming languages support freestanding code blocks and low-level dependency management out of the box.

If you're familiar with unit testing JavaScript with Mocha and VS Code debugging, skip to the section Debugging with Reify. This article was written with no assumptions other than that your system runs Node 11.6+ and VS Code 1.30.2+. This article describes how to use ES modules within a very specific, but common environment: debugging Mocha tests running on Node.js in Microsoft's Visual Studio Code (VS Code). Given their recent emergence from alpha, however, support for ES Modules can vary across tools. Currently supported in modern browsers and Node.js for many months now, ES Modules will over time render various ad-hoc module systems currently in use obsolete. The ES Module standard defines a way to build and assemble JavaScript modules. Debugging ES Modules in Node.js and Mocha Using VS Code

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