Merge pull request #53 from Pouja/bugfix/require-main-is-undefined

fix: Added check if require.main is set

lib/resolve.js

@@ -107,8 +107,15 @@ module.exports = function resolve(dirname) {
 
 	// If the above didn't work, or this module is loaded globally, then
 	// resort to require.main.filename (See http://nodejs.org/api/modules.html)
-	if (alternateMethod || null == appRootPath) {
-		appRootPath = path.dirname(requireFunction.main.filename);
+	if ((alternateMethod || null == appRootPath)) {
+		if (requireFunction.main) {
+			appRootPath = path.dirname(requireFunction.main.filename);
+		} else {
+			// This is the case when app-root-path is bundle'd to a commonjs2 format and is being called from an esm file.
+			// In those cases require.main is undefined (See https://nodejs.org/api/modules.html#accessing-the-main-module)
+			// At that point we can only get the root from looking at the callee
+			appRootPath = path.dirname(process.argv[1]);
+		}
 	}
 
 	// Handle global bin/ directory edge-case