For example: // lib.js export const PI = 3.1415926 export function sum (. Public variables, functions and classes are exposed using export.
CommonJS - the module.exports and require syntax used in Node.jsĪ single, native module standard was therefore proposed in ES6 (ES2015).Įverything inside an ES6 module is private by default, and runs in strict mode (there’s no need for 'use strict'). The options above introduced a variety of competing module definition formats. Transpiling allows you to use alternative syntaxes such as TypeScript or CoffeeScript. Further processing can lint code, remove debugging commands, minify the resulting file, etc. Processing is automated so there’s less chance of human error. Popular options include Babel, Browserify, webpack and more general task runners such as Grunt and Gulp.Ī JavaScript build process requires some effort, but there are benefits: Code is processed to include dependencies and produce a single ES5 cross-browser compatible concatenated file. Module Bundlers, Preprocessors and Transpilersīundlers introduce a compile step so JavaScript code is generated at build time. The systems help, but could become complicated for larger code bases or sites adding standard tags into the mix. Modules are loaded using Ajax methods when required. Systems such as RequireJS and SystemJS provide a library for loading and namespacing other JavaScript libraries at runtime. This solves some performance and dependency management issues, but it could incur a manual build and testing step. 
One solution to problems of multiple tags is to concatenate all JavaScript files into a single, large file. Early JavaScript libraries were notorious for using global function names or overriding native methods. Functions can override others unless appropriate module patterns are used.That could break further JavaScript processing. In the code above, if lib1.js referenced code in lib2.js, the code would fail because it had not been loaded. Dependency management is a manual process.Every script halts further processing while it’s run.HTTP/2 alleviates the issue to some extent, but it doesn’t help scripts referenced on other domains such as a CDN.
Each script initiates a new HTTP request, which affects page performance.The average web page in 2018 uses 25 separate scripts, yet it’s not a practical solution: HTML can load any number JavaScript files using multiple tags: console. Developers therefore resorted to alternative options. It was impossible to directly reference or include one JavaScript file in another. Anyone starting web development a few years ago would have been shocked to discover there was no concept of modules in JavaScript.
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