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inspectpack

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An inspection tool for Webpack frontend JavaScript bundles.

inspectpack provides insight into your webpack-built JS bundles and detailed analysis of opportunites to reduce module sizes, unneeded duplicates, etc. It can be used as a webpack plugin during your compliations or as an offline CLI tool to report on your previous builds.

It is also the engine for the handy webpack-dashboard plugin.

• Plugin
• Command line tool
  • duplicates
  • versions
  • sizes
• Notes, tips, tricks
• Other useful tools

Plugin

The DuplicatesPlugin identifies unnecessarily duplicated code in your webpack bundles with an actionable report to help you trim down wasted bytes.

To get started, install the plugin:

$ npm install --save-dev inspectpack # OR
$ yarn add --dev inspectpack

Then, add the plugin to your webpack.config.js file:

const { DuplicatesPlugin } = require("inspectpack/plugin");

module.exports = {
  // ...
  plugins: [
    // ...
    new DuplicatesPlugin({
      // Emit compilation warning or error? (Default: `false`)
      emitErrors: false,
      // Handle all messages with handler function (`(report: string)`)
      // Overrides `emitErrors` output.
      emitHandler: undefined,
      // List of packages that can be ignored. (Default: `[]`)
      // - If a string, then a prefix match of `{$name}/` for each module.
      // - If a regex, then `.test(pattern)` which means you should add slashes
      //   where appropriate.
      //
      // **Note**: Uses posix paths for all matching (e.g., on windows `/` not `\`).
      ignoredPackages: undefined,
      // Display full duplicates information? (Default: `false`)
      verbose: false
    })
  ]
};

And from there you'll get actionable reports!

A quick tour

Let's see the plugin in action with a quick scenario that has various duplicates from a simple examples repository. (Side note: we've got lots of other interesting inspection scenarios in our test fixtures directory.)

The problem

In this scenario, we have an application that imports a simplified, fake version of lodash in (1) the root application, (2) transitively via a one dependency, and (3) again via a two dependency. Abstractly, the dependency tree (with semver ranges from pacakge.json) looks like:

- my-app:             # Resolved
  - lodash@^4.1.0     # 4.2.3
  - one@1.2.3:        # 1.2.3
    - lodash@^3.0.0   # 3.1.0
  - two@2.3.4:        # 2.3.4
    - lodash@^3.0.0   # 3.1.0

Using modern npm or yarn to install this project gives us the following on-disk node_modules folder (with version resolutions noted):

node_modules          # Resolved
  lodash              # 4.2.3
  one                 # 1.2.3
    node_modules
      lodash          # 3.1.0 (Cannot be collapsed)
  two                 # 2.3.4
    node_modules
      lodash          # 3.1.0 (Cannot be collapsed)

Looking to our resulting bundle we have the following duplicated code sources:

• node_modules/lodash/index.js (4.2.3): This code is similar to the code for 3.1.0.
• node_modules/one/node_modules/lodash/index.js, node_modules/two/node_modules/lodash/index.js (3.1.0): These two files are identical code sources. They are only included twice in the bundle because npm/yarn could not flatten the dependencies during installation.

So, we've got inefficient code that we discovered via a manual inspection. Wouldn't it be nice to have a report that specifically highlighted problems like these with useful information?

... enter the DuplicatesPlugin.

Diagnosing duplicates

Simple report

With our plugin enabled in the standard configuration:

new DuplicatesPlugin()

we get a summary report of the duplicates upon running the webpack command:

WARNING in Duplicate Sources / Packages - Duplicates found! ⚠️

* Duplicates: Found 2 similar files across 3 code sources (both identical + similar)
  accounting for 703 bundled bytes.
* Packages: Found 1 packages with 2 resolved, 3 installed, and 3 depended versions.

## bundle.js
lodash (Found 2 resolved, 3 installed, 3 depended. Latest 4.2.3.)
  3.1.0 ~/one/~/lodash
    scenario-new-webpack-new-npm-unflattened@* -> one@1.2.3 -> lodash@^3.0.0
  3.1.0 ~/two/~/lodash
    scenario-new-webpack-new-npm-unflattened@* -> two@2.3.4 -> lodash@^3.0.0
  4.2.3 ~/lodash
    scenario-new-webpack-new-npm-unflattened@* -> lodash@^4.1.0

Breaking down this report, we get a webpack "warning" emitted by default with an initial summary of the report.…