node-get-project-root/src/index.js

'use strict';

const fs = require("fs");
const path = require("path");
const defaultValue = require("default-value");

let defaultCheckers = {
	"package.json": function(directory) {
		let parentPackageFile = path.join(directory, `..${path.sep}..${path.sep}package.json`);

		try {
			fs.accessSync(parentPackageFile);
			return false;
		} catch (err) {
			return true;
		}
	},
	"vcs": function(directory) {
		let files = fs.readdirSync(directory);

		return [".git", ".hg"].some((target) => {
			return (files.indexOf(target) !== -1);
		});
	}
}

function reachedRoot(candidatePath) {
	/* Returns true if we hit the root of the filesystem; like / or C:\ */
	return /^(?:\/|a-z:\\)$/i.test(candidatePath);
}

module.exports = function(options) {
	let currentPath = defaultValue(options.basePath, __dirname);
	let checker = defaultValue(options.checker, "package.json");

	if (typeof checker === "string") {
		if (defaultCheckers[checker] != null) {
			checker = defaultCheckers[checker];
		} else {
			throw new Error("No such checker exists.");
		}
	}

	/* Locate the first thing that has a package.json, in case we're in a
	 * subdirectory within a module. Only after we've found the nearest
	 * package.json, we will start using the checker.
	 */

	let baseFound = false;

	while (baseFound === false) {
		baseFound = (fs.readdirSync(currentPath).indexOf("package.json") !== -1);

		if (reachedRoot(currentPath)) {
			throw new Error("Reached filesystem root without encountering a module");
		}

		if (baseFound === false) {
			currentPath = path.join(currentPath, "..");
		}
	}

	let rootFound = false;

	while (rootFound === false) {
		rootFound = checker(currentPath);

		if (rootFound !== true && rootFound !== false) {
			throw new Error("Checker must always return either true or false");
		}

		if (reachedRoot(currentPath)) {
			throw new Error("Reached filesystem root without encountering the project root");
		}

		if (rootFound === false) {
			currentPath = path.join(currentPath, `..${path.sep}..`);
		}
	}

	return currentPath;
}