@nativescript/hook

@nativescript/hook

This module gives you an easier way to install hooks into NativeScript projects when using the tns install <module> command. A project hook is some sort of script that is configured to be executed when the NativeScript CLI executes some action.

Hooks go into the hooks/ folder of a project. For example, when tns prepare ... is executed, all script files in the hooks/before-prepare/ and hooks/after-prepare/ folders are executed, as well.

This module simplifies the process of installing the scripts into the right project folder.

How to use

Describe the hooks

First, add a description of your hooks to the module's package.json. Here's an example:

{
  "nativescript": {
    "hooks": [
      {
        "type": "before-prepare",
        "script": "lib/before-prepare.js"
      }
    ]
  },
}

The above specifies that the script lib/before-prepare.js should be executed when the tns prepare ... command is executed. the "type" property specifies the type of the hook to install. The "script" property specifies the path to the script to execute. You can add more hooks by extending the "hooks" array.

Install the hooks

Add a post-install and pre-uninstall script to your package.json, if you haven't done so already:

  "scripts": {
    ...
    "postinstall": "node postinstall.js",
    "preuninstall": "node preuninstall.js"
  },

The post-install script (postinstall.js in the example) should contain the following line:

require('@nativescript/hook')(__dirname).postinstall();

The pre-uninstall script (preuninstall.js in the example) should contain the following line:

require('@nativescript/hook')(__dirname).preuninstall();

These two hooks will take care of installing and removing the hooks from the NativeScript project, when your module is installed or uninstalled.

tns install <module>

NativeScript modules that install hooks are intended to be installed using the tns install <module> command, not through npm directly. During module installation the NativeScript CLI provides information to the post-install script where to put the hooks. The following environment variables are defined when installing through tns install <module>:

• TNS_HOOKS_DIR - the directory where the hooks should be installed. It may or may not exist.
• TNS_PROJECT_DIR - the current project directory.

Modules installed this way can be uninstalled simply by running npm rm --save-dev.

In-process hooks

By default, hooks are executed in a child process and execution continues when the child process dies. This gives you flexibility when writing your hooks, but doesn't allow you to use any of the services of the CLI.

To that end, in-process hooks allow you to execute your hooks in such a way so that you can use any of the services available from the injector. In-process hooks work only for JavaScript hooks. To enable in-process execution, all you need to have is a module.exports = ... statement in the hook. For example, if the hook script is:

module.exports = function($logger) {
};

Then, the hook script will be require'd by the CLI and the exported function will be called through the injector.

Hooks can take a special injected argument named hookArgs:

module.exports = function(hookArgs) {
};

hookArgs is a hash containing all the arguments passed to the hooked method. For example, the prepare hook is activated by the CLI method preparePlatform(platform: string). Here, the hook will get the value of the platform argument in the hookArgs.platform property.

If you execute asynchronous code in your hook, you need to return a promise, otherwise execution will continue before your hook completes:

var mkdirp = require('mkdirp');
module.exports = function($logger) {
  return new Promise(function(resolve, reject) {
      mkdirp('somedir', function(err) {
          if (err) {
            reject(err);
          else {
            resolve();
          }
        })
    });
}

And finally, when installing in-process hooks through this module, you need to explicitly specify that using the inject property of the script descriptor in the package.json:

{
  "nativescript": {
    "hooks": [
      {
        "type": "after-prepare",
        "script": "lib/after-prepare.js",
        "inject": true
      }
    ]
  },
}

You have the ability to define a custom name to your hook in package.json, this attribute is optional and defaults to the plugin package name:

{
  "nativescript": {
    "hooks": [
      {
        "type": "after-prepare",
        "script": "lib/after-prepare.js",
        "name": "my-custom-hook"
      }
    ]
  },
}