refactor: remove some duplication

lib/getManifest.js

@@ -50,19 +50,16 @@ function getManifest(path) {
 		throw new SyntaxError(`Package name must be non-empty string: "${path}"`);
 
 	// Check dependencies.
-	if (!manifest.hasOwnProperty("dependencies")) manifest.dependencies = {};
-	else if (typeof manifest.dependencies !== "object")
-		throw new SyntaxError(`Package dependencies must be object: "${path}"`);
+	const checkDeps = (scope) => {
+		if (!manifest.hasOwnProperty(scope)) manifest[scope] = {};
+		else if (typeof manifest[scope] !== "object")
+			throw new SyntaxError(`Package ${scope} must be object: "${path}"`);
+	};
 
-	// Check devDependencies.
-	if (!manifest.hasOwnProperty("devDependencies")) manifest.devDependencies = {};
-	else if (typeof manifest.devDependencies !== "object")
-		throw new SyntaxError(`Package devDependencies must be object: "${path}"`);
-
-	// Check peerDependencies.
-	if (!manifest.hasOwnProperty("peerDependencies")) manifest.peerDependencies = {};
-	else if (typeof manifest.peerDependencies !== "object")
-		throw new SyntaxError(`Package peerDependencies must be object: "${path}"`);
+	checkDeps("dependencies");
+	checkDeps("devDependencies");
+	checkDeps("peerDependencies");
+	checkDeps("optionalDependencies");
 
 	// Return contents.
 	return manifest;