squoosh/config/watch-timestamps-plugin.js

const fs = require('fs');

module.exports = class WatchTimestampsPlugin {
	constructor(patterns) {
		this.patterns = patterns;
	}

	apply(compiler) {
		compiler.plugin('watch-run', (watch, callback) => {
			let patterns = this.patterns;
			let timestamps = watch.fileTimestamps || watch.compiler.fileTimestamps;

			Object.keys(timestamps).forEach(filepath => {
				if (patterns.some(pat => pat instanceof RegExp ? pat.test(filepath) : filepath.indexOf(pat) === 0)) {
					let time = fs.statSync(filepath).mtime;
					if (timestamps instanceof Map) timestamps.set(filepath, time);
					else timestamps[filepath] = time;
				}
			});
			callback();
		});
	}
};