js-to-js

ExpressJS template engine to render JavaScript from JavaScript to avoid inlined code and allow strict and safe Content-Security-Policy.

Live demo at js-to-js.herokuapp.com

Read the following blog posts

• Disable inline JavaScript for security
• JavaScript to JavaScript template language

Install

npm install --save js-to-js

Simple example

Inside your ExpressJS server use it as a template engine for 'js' files

var express = require('express');
var app = express();
 
var viewsFolder = join(__dirname, 'views');
app.set('views', viewsFolder);
 
var jsToJs = require('js-to-js');
app.engine('js', jsToJs);
app.locals.pretty = true; // render pretty output, don't minify for now
 
// when asked for 'js/analytics-config.js', render it dynamically
app.get('/js/analytics-config.js', function (req, res) {
  // use this for correct content-type -
  // Express will think it is text/html by default
  res.setHeader('content-type', 'application/javascript');
  // this path is WRT views folder
  res.render('js/analytics-config.js', {
    // use any run-time values, for example from config
    analyticsId: '4xx-xxxxx'
  });
});

The input object file

By default we expect the input views to be plain CommonJS modules exporting and object. The files are loaded using NodeJS require call. For example the views/js/analytics-config.js file might be just an object with single property.

module.exports = {
  analyticsId: 'default-id'
};

The CommonJS format is simple to use and test.

The rendered script file

The rendered file will have a single variable declared with the value being the object from the input file, but the values replaced / extended using dynamic values.

The name of the variable will be the kebab case of the base name of the requested file. For example if the input file is views/js/analytics-config.js and rendered using options

{
  analyticsId: '0123456',
  user: 'john@gmail.com',
  UUID: 'abcd012345'
}

then the produced JavaScript file will contain only the following code

var analyticsConfig = {
  analyticsId: '0123456'
};

Limiting the keys to only the ones already in the input file is done for modularity.

Wrapping a function example

If you need to inject values into a 3rd party script, like Google Analytics, export a function that expects options argument. The function will be wrapped in an IIFE with actual arguments passed in.

// analytics.js in the views folders
module.exports = function (options) {
  initAnalytics(options.userId);
};

You route can be setup exactly like before

var userId = 'xx-yy-bb';
app.get('/js/analytics.js', function (req, res) {
  res.setHeader('content-type', 'application/javascript');
  res.render('analytics.js', {
    userId: userId
  });
});

At runtime it will be rendered back to the user something like this

(function (options) {
  initAnalytics(options.userId);
}({ userId: 'xx-yy-bb' }));

Using as middleware

Sometimes you have a simple object with settings you just want to send to the client, but generate a script variable. Just use js-to-js as middleware generator.

var jsToJs = require('js-to-js');
app.get('/js/demo-config-object.js',
  jsToJs('demoConfig', { foo: 42, bar: 21 }));

Whenever the client requests /js/demo-config-object.js the server will respond with dynamically generated script with the following contents

var demoConfig = { foo: 42, bar: 21};

Working example / demo

This repository bahmutov/js-to-js contains fully working example in the demo subfolder. You can run it locally using

git clone git@github.com:bahmutov/js-to-js.git
cd js-to-js/demo
npm install
node index.js
open http://localhost:3000/index.html

You can also see it deployed at js-to-js.herokuapp.com.

Small print

Author: Gleb Bahmutov © 2015

• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Spread the word: tweet, star on github, etc.

Support: if you find any problems with this module, email / tweet / open issue on Github

MIT License

Copyright (c) 2015 Gleb Bahmutov

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.