flow like the river

BACK_BACK/node_modules/graphql/utilities/assertValidName.js.flow

@@ -0,0 +1,34 @@
+// @flow strict
+import devAssert from '../jsutils/devAssert';
+
+import { GraphQLError } from '../error/GraphQLError';
+
+const NAME_RX = /^[_a-zA-Z][_a-zA-Z0-9]*$/;
+
+/**
+ * Upholds the spec rules about naming.
+ */
+export function assertValidName(name: string): string {
+  const error = isValidNameError(name);
+  if (error) {
+    throw error;
+  }
+  return name;
+}
+
+/**
+ * Returns an Error if a name is invalid.
+ */
+export function isValidNameError(name: string): GraphQLError | void {
+  devAssert(typeof name === 'string', 'Expected name to be a string.');
+  if (name.length > 1 && name[0] === '_' && name[1] === '_') {
+    return new GraphQLError(
+      `Name "${name}" must not begin with "__", which is reserved by GraphQL introspection.`,
+    );
+  }
+  if (!NAME_RX.test(name)) {
+    return new GraphQLError(
+      `Names must match /^[_a-zA-Z][_a-zA-Z0-9]*$/ but "${name}" does not.`,
+    );
+  }
+}