Fine‑Tuning Bower Installs: Using the `ignore` Field to Skip Unwanted Files

Why the Extra Files Matter

When a front‑end project pulls in a library via Bower, the tool downloads the entire package that lives on the registry. That includes source code, tests, documentation, and sometimes large binary assets. For a team that only needs the compiled JavaScript and CSS, downloading everything inflates the bower_components directory, slows installations, and can even introduce unnecessary security exposure.

What the ignore Field Does

The ignore array in bower.json accepts minimatch patterns. Bower evaluates each pattern against the files in the package and omits any that match. This filtering happens before the files are extracted into bower_components, so the network traffic and disk usage are both reduced.

Typical patterns include:

• **/*.md – all Markdown documentation
• test/** – entire test directory
• src/** – raw source files that are not needed in the browser
• *.zip – any bundled archives

How to Declare an ignore Array

Below is a minimal bower.json for a package that wants to keep only the compiled assets:

{
  "name": "awesome-lib",
  "version": "1.2.3",
  "main": "dist/awesome-lib.min.js",
  "ignore": [
    "**/*.md",
    "test/**",
    "src/**",
    "*.zip"
  ]
}

When another project declares a dependency on awesome-lib, Bower will skip any files matching those patterns. The resulting bower_components/awesome-lib directory will contain only dist/awesome-lib.min.js and any other files that are not ignored.

Verifying the Effect

After running bower install, inspect the package directory:

# Run from the project root
$ ls bower_components/awesome-lib
# Expected output: dist/awesome-lib.min.js

Alternatively, use Bower’s list command to view the resolved tree:

$ bower list --depth=0
# Should show awesome-lib with only the expected files

If you see files you intended to ignore, double‑check the patterns for typos or missing leading slashes. Remember that patterns are matched relative to the package root, not the project root.

Trade‑Offs and Caveats

• Maintenance Burden – Every time the package’s file layout changes, you may need to update the ignore patterns. A misconfigured ignore can accidentally strip required assets.
• Legacy Packages – Some older Bower packages do not declare a main field. In those cases, Bower falls back to heuristics that may include ignored files if the heuristics cannot determine the correct entry point.
• Security Considerations – Bower itself is unmaintained. While ignore reduces the surface area, you still need to audit the packages you pull in for vulnerabilities.

When to Use ignore and When Not To

Use ignore when:

• Packages are large and contain many ancillary files.
• You control the package and can guarantee that the ignored files are truly unnecessary.
• You want to speed up CI pipelines by reducing download size.

Avoid ignore when:

• The package’s documentation is needed for local development or debugging.
• Future maintainers might rely on the omitted files (e.g., build scripts).

Actionable Takeaway

To keep your Bower installations lean:

1. Add an ignore array to your bower.json with clear minimatch patterns.
2. Run bower install and immediately ls the package directory to confirm the expected files are present.
3. Commit the updated bower.json and bower_components lock file to your repository.
4. Monitor the size of bower_components over time; if it grows unexpectedly, revisit your ignore rules.

By thoughtfully configuring ignore, you reduce bandwidth, disk usage, and the risk of accidentally shipping test code or documentation to production.