Plugin development

To create a plugin for semantic-release, you need to decide which parts of the release lifecycle are important to that plugin. For example, it is best to always have a verify step because you may be receiving inputs from a user and want to make sure they exist. A plugin can abide by any of the following lifecycles:

• verify

• prepare

• publish

• success

• fail

semantic-release will require the plugin via node and look through the required object for methods named like the lifecyles stated above. For example, if your plugin only had a verify and success step, the main file for your object would need to export an object with verify and success functions.

In addition to the lifecycle methods, each lifecyle is passed two objects:

1. pluginConfig - an object containing the options that a user may pass in via their release.config.js file (or similar)

2. context - provided by semantic-release for access to things like env variables set on the running process.

For each lifecycle you create, you will want to ensure it can accept pluginConfig and context as parameters.

Creating a Plugin Project

It is recommended that you generate a new project with yarn init. This will provide you with a basic node project to get started with. From there, create an index.js file, and make sure it is specified as the main in the package.json. We will use this file to orchestrate the lifecycle methods later on.

Next, create a src or lib folder in the root of the project. This is where we will store our logic and code for how our lifecycle methods work. Finally, create a test folder so you can write tests related to your logic.

We recommend you setup a linting system to ensure good javascript practices are enforced. ESLint is usually the system of choice, and the configuration can be whatever you or your team fancies.

Exposing Lifecycle Methods

In your index.js file, you can start by writing the following code

const verifyConditions = require('./src/verify');

let verified;

/**
 * Called by semantic-release during the verification step
 * @param {*} pluginConfig The semantic-release plugin config
 * @param {*} context The context provided by semantic-release
 */
async function verify(pluginConfig, context) {
  await verifyConditions(pluginConfig, context);
  verified = true;
}

module.exports = { verify };

Then, in your src folder, create a file called verify.js and add the following

const AggregateError = require('aggregate-error');

/**
 * A method to verify that the user has given us a slack webhook url to post to
 */
module.exports = async (pluginConfig, context) => {
  const { logger } = context;
  const errors = [];

  // Throw any errors we accumulated during the validation
  if (errors.length > 0) {
    throw new AggregateError(errors);
  }
};

As of right now, this code won't do anything. However, if you were to run this plugin via semantic-release, it would run when the verify step occurred.

Following this structure, you can create different steps and checks to run through out the release process.

Supporting Options

Let's say we want to verify that an option is passed. An option is a configuration object that is specific to your plugin. For example, the user may set an option in their release config like:

{
    prepare: {
        path: "@semantic-release/my-special-plugin"
        message: "My cool release message"
    }
}

This message option will be passed to the pluginConfig object mentioned earlier. We can use the validation method we created to verify this option exists so we can perform logic based on that knowledge. In our verify file, we can add the following:

const { message } = pluginConfig;

if (message.length) {
    //...
}

Supporting Environment Variables

Similar to options, environment variables exist to allow users to pass tokens and set special URLs. These are set on the context object instead of the pluginConfig object. Let's say we wanted to check for GITHUB_TOKEN in the environment because we want to post to GitHub on the user's behalf. To do this, we can add the following to our verify command:

const { env } = context;

if (env.GITHUB_TOKEN) {
    //...
}