child_process: adds normalization for fork function arguments

Closes: nodejs#20749

lib/child_process.js

@@ -58,24 +58,38 @@ function stdioStringToArray(option) {
   }
 }
 
+function normalizeForkArguments(args, options) {
+  if (Array.isArray(args)) {
+    args = args.slice(0);
+  } else if (options !== undefined &&
+             (args === undefined ||
+              args === null ||
+              typeof args !== 'object')
+  ) {
+    throw new ERR_INVALID_ARG_TYPE('args', 'array', args);
+  } else {
+    options = args;
+    args = [];
+  }
+
+  if (options === undefined)
+    options = {};
+  else if (options === null || typeof options !== 'object')
+    throw new ERR_INVALID_ARG_TYPE('options', 'object', options);
+
+  return {
+    args,
+    options
+  };
+}
+
 exports.fork = function fork(modulePath /* , args, options */) {
 
   // Get options and args arguments.
   var execArgv;
-  var options = {};
-  var args = [];
-  var pos = 1;
-  if (pos < arguments.length && Array.isArray(arguments[pos])) {
-    args = arguments[pos++];
-  }
-
-  if (pos < arguments.length && arguments[pos] != null) {
-    if (typeof arguments[pos] !== 'object') {
-      throw new ERR_INVALID_ARG_VALUE(`arguments[${pos}]`, arguments[pos]);
-    }
-
-    options = util._extend({}, arguments[pos++]);
-  }
+  var opts = normalizeForkArguments(arguments[1], arguments[2]);
+  var options = opts.options;
+  var args = opts.args;
 
   // Prepare arguments for fork:
   execArgv = options.execArgv || process.execArgv;