error definition improved

frontend-js/src/main/js/InvalidArgumentError.js

@@ -10,4 +10,6 @@ function InvalidArgumentError(message) {
   this.stack = (new Error()).stack;
 }
 
+InvalidArgumentError.prototype = new Error
+
 module.exports = InvalidArgumentError;

frontend-js/src/main/js/InvalidCredentialsError.js

@@ -10,4 +10,6 @@ function InvalidCredentialsError(message) {
   this.stack = (new Error()).stack;
 }
 
+InvalidCredentialsError.prototype = new Error
+
 module.exports = InvalidCredentialsError;

frontend-js/src/main/js/NetworkError.js

@@ -16,4 +16,6 @@ function NetworkError(message, connectionParams) {
   this.content = connectionParams.content;
 }
 
+NetworkError.prototype = new Error
+
 module.exports = NetworkError;