refactor: create common validation function

utils/validate.js

@@ -0,0 +1,13 @@
+const validCharsRE = /^[a-zA-Z0-9\-_+]+$/;
+const invalidCharError = {
+  valid: false,
+  error: 'contains invalid characters'
+};
+const validationSuccess = { valid: true, error: null };
+const usernameTooShort = { valid: false, error: 'is too short' };
+
+exports.validate = str => {
+  if (str.length < 3) return usernameTooShort;
+  if (!validCharsRE.test(str)) return invalidCharError;
+  return validationSuccess;
+};