Rollup will combine the helpers in a single block at the top of your bundle. This rollup plugin automatically deduplicates those helpers, keeping only one copy of each one used in the output bundle. In some cases Babel uses helpers to avoid repeating chunks of code – for example, if you use the class keyword, it will use a classCallCheck function to ensure that the class is instantiated correctly.īy default, those helpers will be inserted at the top of the file being transformed, which can lead to duplication. babelrc files, relying instead on the configuration you pass in. Use babelrc: false to prevent Babel from using local (i.e. Consumers of your library should not have to transpile your ES6 code, any more than they should have to transpile your CoffeeScript, ClojureScript or TypeScript. We encourage library authors not to distribute code that uses untranspiled ES6 features (other than modules) for this reason. babelrc files or mismatched versions of Babel. If you have a dependency that exposes untranspiled ES6 source code that doesn't run in your target environment, then you may need to break this rule, but it often causes problems with unusual. Ideally, you should only be transforming your source code, rather than running all of your external dependencies through Babel (to ignore external dependencies from being handled by this plugin you might use exclude: 'node_modules/**' option). This is used to validate some misconfiguration errors, but for sufficiently big projects it can slow your build times so if you are confident about your configuration then you might disable those checks with this option. This is the default Babel behavior as Babel operates on isolated files - however, as Rollup is a bundler and is project-aware (and therefore likely operating across multiple input files), the default of this plugin is "bundled".īefore transpiling your input files this plugin also transpile a short piece of code for each input file. Helpers will be inserted in each file using this option. Used in combination with 'inline' - this is not recommended. It will reference helpers on global babelHelpers object. 'external' - use this only if you know what you are doing.Useful especially if you bundle an application code. 'bundled' - you should use this if you want your resulting bundle to contain those helpers (at most one copy of each).This can be accomplished via regex ( external: or a function ( external: id => It's important to not only specify external: since the helpers are imported from nested paths (e.g and Rollup will only exclude modules that match strings exactly. Don't forget to tell Rollup to treat the helpers imported from within the module as external dependencies when bundling for cjs & es formats. It has to be used in combination with and you should also specify as dependency of your package. 'runtime' - you should use this especially when building libraries with Rollup.We recommend to follow these guidelines to determine the most appropriate value for your project: It is recommended to configure this option explicitly (even if with its default value) so an informed decision is taken on how those babel helpers are inserted into the code. Type: 'bundled' | 'runtime' | 'inline' | 'external' If you want to transpile TypeScript files with this plugin it's essential to include. Import ) extensionsĭefault: Īn array of file extensions that Babel should transpile. This plugin requires an LTS Node version (v10.0.0+) and Rollup v1.20.0+. Using Rollup with makes the process far easier. In the second case, transpiling is likely to be slower, because transpiling a large bundle is much more work for Babel than transpiling a set of small files.Įither way, you have to worry about a place to put the intermediate files, and getting sourcemaps to behave becomes a royal pain. run the code through Rollup first, and then pass it to Babel.īoth approaches have disadvantages – in the first case, on top of the additional configuration complexity, you may end up with Babel's helpers (like classCallCheck) repeated throughout your code (once for each module where the helpers are used).run the code through Babel first, being careful to exclude the module transformer, or.If you're using Babel to transpile your ES6/7 code and Rollup to generate a standalone bundle, you have a couple of options: A Rollup plugin for seamless integration between Rollup and Babel.
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