Polyfiller

Scans JavaScript files and emits list of used features that Polyfill.io can polyfill.

• Defaults to Polyfill.io library version 4.8.0, but can also work with 3.111.0.
• Emits array of feature names to stdout or to JSON or YAML.

Use the detected feature list to create a Polyfill.io URL requesting polyfills for just those features.

Features are detected by parsing JavaScript files into an AST, not with brittle regexes.

Quickstart

npm install --save-dev @convinciblemedia/polyfiller
npx polyfiller 'dist/**/*.js'

Arguments:

• <glob-pattern>: The JavaScript files to scan.

Options:

• --output, -o <path>: Write the detected feature array to a file.
• --format, -f <json|yml|yaml>: Choose the output format. If omitted, Polyfiller infers it from the output path extension, then falls back to JSON.
• --library-version <version>: Target a specific polyfill-library version.
• --report: Print the per-file and per-feature breakdowns to stderr.
• --help, -h: Show CLI help.
• --version: Print the CLI package version.

When no output file is given:

• stdout contains only the machine-readable feature array.
• stderr contains warnings for skipped files and the human-readable report if enabled.

That split is deliberate, so you can pipe stdout into another command without having to strip logs out of it.

Output

JSON output looks like this:

[
	"Promise",
	"Promise.any",
	"URL",
	"URL.prototype.toJSON"
]

YAML output looks like this:

- "Promise"
- "Promise.any"
- "URL"
- "URL.prototype.toJSON"

The output array contains the direct feature names detected in your JavaScript, using the same names as Polyfill.io.

Supported Versions

The published package ships with built-in support for these Polyfill.io library versions:

• 3.111.0
• 4.8.0

CLI consumers cannot point Polyfiller at arbitrary custom feature lists. Support only expands when the library itself ships another bundled x.y.z.txt file in a later release.

If a bundled version contains features that Polyfiller does not currently know how to detect from JavaScript, those features are simply never emitted.

Programmatic Usage

import { analysePolyfills } from '@convinciblemedia/polyfiller';

const result = await analysePolyfills({
	cwd: process.cwd(),
	pattern: 'dist/**/*.js',
	targetVersion: '4.8.0'
});

console.log(result.detectedFeatures);
console.log(result.warnings);

The returned object includes:

• targetVersion
• detectedFeatures
• warnings
• featuresByFilePath
• fileCountsByFeature
• matchedFileCount