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Version: v3

Output Targets

One of the more powerful features of the compiler is its ability to generate various builds depending on "how" the components are going to be used. Stencil is able to take an app's source and compile it to numerous targets, such as a webapp to be deployed on an http server, as a third-party component lazy-loaded library to be distributed on npm, or a vanilla custom elements bundle. By default, Stencil apps have an output target type of www, which is best suited for a webapp.

Output Target Types:​

Example:​

import { Config } from '@stencil/core';

export const config: Config = {
  outputTargets: [
    {
      type: 'dist'
    },
    {
      type: 'www'
    }
  ]
};

Differential Bundling​

It's also important to note that the compiler will automatically generate the numerous bundles in order to support "differential bundling". What this means is that during production builds, Stencil will generate code for both modern browsers, and legacy browsers (IE11) from the same source code. The advantage of differential bundling is that modern browsers can avoid all the polyfills and bloated legacy JavaScript, and use the modern APIs already baked into the browser.

In the example below there are two script tags, however, only one of them will be requested by the user. For IE11 users, they'll download the app.js file which is in the ES5 syntax and has all the polyfills. For users on modern browsers, they will only download the app.esm.js file which uses up-to-date JavaScript features such as ES modules, dynamic imports, async/await, Classes, etc.

note

buildEs5 must be set to true to generate the IE11 ES5 file

<script type="module" src="/build/app.esm.js"></script>
<script nomodule src="/build/app.js"></script>
info

As of Stencil v3, legacy browser support is deprecated, and will be removed in a future major version of Stencil.

Primary Package Output Target Validation​

If validatePrimaryPackageOutputTarget: true is set in your project's Stencil config Stencil will attempt to validate certain fields in your package.json that correspond with the generated distribution code. Because Stencil can output many different formats from a single project, it can only validate that the package.json has field values that align with one of the specified output targets in your project's config. So, Stencil allows you to designate which output target should be used for this validation and thus which will be the default distribution when bundling you project.

This behavior only affects a small subset of output targets so a flag exists on the following targets that are eligible for this level of validation: dist, dist-types, dist-collection, and dist-custom-elements. For any of these output targets, you can configure the target to be validated as follows:

stencil.config.ts
import { Config } from '@stencil/core';
export const config: Config = {
  ...,
  outputTargets: [
    {
      type: 'dist',
      // This flag is what tells Stencil to use this target for validation
      isPrimaryPackageOutputTarget: true,
      ...
    },
    ...
  ],
  // If this is not set, Stencil will not validate any targets
  validatePrimaryPackageOutputTarget: true,
};
note

Stencil can only validate one of these output targets for your build. If multiple output targets are marked for validation, Stencil will use the first designated target in the array and ignore all others.

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