# Cordova Hooks

Cordova is extremely powerful, but it’s not always obvious. Hooks are a good example of this. Hooks let you attach to specific steps in Cordovas processes and run scripts before and after certain things occur.

In this post, we’ll go over a simple way to copy a config file before a build is started, and show a message in the console once the build has completed.

There are two different ways you can create Cordova hooks. You can either simply put a .js file in a subdirectory of the hooks directory Cordova provides, or you can define one in the config.xml file. Lets go over the subdirectory method first, since it’s the simplest.

Here is a sample project on github that shows how to copy a config file before the build starts, and spits out a fun message when the build is complete.

## Hooks Subdirectories

When you build an Ionic or Cordova project using the command line tools, scaffolding comes along with it to aid development. One of the directories provided is the hooks directory. In this there is a README.md file that explains the type of subdirectories available for hooks.

The directory names match the time you want your hook to run. For example, if I want a script to run after my build is complete, I would create an after_build directory and place a .js file in it.

There are two special things you need to do with your .js file once you add it. First, you need to make sure the first line is #!/usr/bin/env node and you must make sure the file is executable. On my windows machine, I didn’t have to set any files as executable specifically, so that piece might be a Unix only scenario.

Inside your .js file you can do anything you want. From there, it’s just a regular node script so let your imagination go wild.

## Config.xml Hooks

Now lets handle something a little more tricky. Lets make a hook that copies over a config file containing our Ionic environment settings before our project builds.

First, create a folder under www called config. Inside that, create three .js files named dev.js, stage.js and prod.js In each of those files, create an AngularJS constant similar to the following:

angular.module('constants',[])
.constant('ENV',{
name: 'dev',
baseUrl: 'http://dev.whatever.com',
magicKey: '123-456-789',
someOtherThing: {
id: 1,
arrayOfSomeStuff: [1,2,3,4,5]
}
});


We’re going to copy one of those files, depending on the passed parameter to the command line, to the file www/js/config.js. To make sure we can use this constant, add config.js to your index.html file, and in the controllers.js file include the constants module in the starter.controllers module. Now you can use ENV in your controllers and services.

Now, we’ll just create a script in our hooks base directory, not in any subdirectory, named updateConfig.js

Next, we’ll open up our config.xml file and add the following tag: <hook type="before_build" src="hooks/updateConfig.js"/>

That tag should go right before the <platform> tag in config.xml. The type attribute is the type of hook we’re setting up. The values here are the same as any subdirectory you would create under the hooks directory. The src attribute tells the system where to find the file to run.

Now, the contents of the file is going to be a bit different than our after build hook. When defining a hook from the config.xml file, you’re actually exporting a function that Cordova will call.

Cordova will pass a parameter to your function called context. This lets you have access to far more properies about your project than you have by just putting a .js file in a subdirectory. Fire off a console.log(context) to see the magic happen.

You can pass parameters to your Cordova build command line calls by prefixing them with --. For example, in our script, if we wanted to do a production level build, we’d use the command cordova build android --prod.

Here is what the updateConfig.js file will look like to copy the correct config file.


//Here we're going to copy our config based on our options. Dev by default

// GOTCHAS - This assumes there will be only one -- style option in the command line.
// More code would have to be added to handle more options.
// Perhaps parse them using this: https://github.com/bcoe/yargs

var fs = require('fs');

module.exports = function(context){

//Uncomment this to see other options the context gives you.
//console.log(context);

//This gives us promises!
var Q = context.requireCordovaModule('q');

var defer = Q.defer();
var envSelect = context.cmdLine.split('--');
var envName = 'dev';

if(envSelect.length > 1){
envName = envSelect[1];
}

var projectRoot = context.opts.projectRoot;

var sourceFile = projectRoot + '/www/config/' + envName + '.js';
var destFile = projectRoot + '/www/js/config.js';

var writeStream = fs.createWriteStream(destFile);

defer.reject('Could not copy\n'+sourceFile +'\nto\n' + destFile);
});

writeStream.on('error', function(err){
defer.reject('Could not copy\n'+sourceFile +'\nto\n' + destFile);
});

writeStream.on('close', function(){
console.log('Environment ' + envName + ' loaded successfully!');
defer.resolve();
});