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Webpack Notes

Introduction

This work package replaces Grunt-based concatenation and minification and testing, with Webpack, providing the following advantages:

  1. Clearer and more modular dependency management using import/export
  2. Modular code is easier to unit-test
  3. On-the-fly compilation and serving of files
  4. Facility for splitting distribution into several modules so that less commonly used features can be lazy-loaded (TODO)
  5. Possibility of upgrading javascript ES6 by introducing babel compiler (TODO)

The emphasis is this work-package has been to make minimal and localized changes to the core code to factilitate merging back into the main branch. However the interdependencies between the different files were quite complicated and untangling them with minimal impact hasn't been easy.

Assuming the PR is accepted and merged into the main branch, there will be potential for a lot more refactoring and simplification of the codebase.

Useful docs

https://webpack.js.org/guides/

I loosely based the structure of the webpack config files on this article angular webpack guide.

Summary of Changes

  1. Refactored code to use import / export to specify dependencies instead of relying on concatenation

  2. Replaced Grunt with Webpack tasks - setting up files in ./config for production/development/test builds

  3. Replaced jshint with eslint - eslint better supports newer js features and its config files can be picked up automatically by IDEs such as VS Code, providing intellisense linting support

  4. Created some unit test stub implementations

  5. package.json:

    1. Replaced all grunt-based scripts
    2. Removed all grunt dev-dependencies (also package.lock.json)

  6. updated docs

  7. removed other references to Grunt

TODO

  1. implement headless unit testing and integrate into Travis

Future Work

Polyfills

I have included the old ie9.js file in the build even though it breaks the modularity afforded by webpack. Webpack has its own infrastructure for providing polyfills in an efficient way and we should look into migrating to that.

Other Package Optimisations

Currently all code is compiled into a single bundle. We should look at splitting less commonly-used code into lazy-loaded bundles to allow speedier loading of core code

General Refactoring

Now that dependencies in the code are clearer, opportunites for improving structure and readability of code should reveal themselves.

Expansion of Unit Test Coverage

I have provided some very basic unit-test stubs. It should now be much easier to unit test code so we should:

  1. Ensure that before editing existing code, we write unit-tests to cover our assumptions about its functions
  2. When writing new code, adopt a TDD approach - IE, write tests before writing the implementation

Upgrade to ES6

Javascript ES6 provides many useful language features which make for clearer, less error-prone code including:

  1. classes (which would allow us to get rid of homegrown class.js)
  2. template literals
  3. let/const providing better variable scoping

It is fairly easy to introduce transpilation from ES6 via Webpack to enable these features - I'd recommend doing so.

Editors

JSONEditor.defaults

The base class editor had a dependency on the translate and callbacks properties of JSONEditor.defaults.

Aditionally, all editors had a single dependency on JSONEditor via the .defaults.options property, accessed in the build() or afterInputReady() method. In each case, these options are merged with the user options using a virtually identical formula. Would it be worth looking at creating a base class helper method for this merge, to keep things DRY?.

For now I have passed in JSONEditor.defaults as defaults.