webpack检测webpack cli是否安装的方法

const isInstalled = packageName => {
	if (process.versions.pnp) {
		return true;
	}

	const path = require("path");
	const fs = require("graceful-fs");

	let dir = __dirname;

	do {
		try {
			if (
				fs.statSync(path.join(dir, "node_modules", packageName)).isDirectory()
			) {
				return true;
			}
		} catch (_error) {
			// Nothing
		}
	} while (dir !== (dir = path.dirname(dir)));

	return false;
};

　　通过do while循环，往上面一层层的查找