The "Error" Object Type - Runtime Exceptions

This section provides a quick description and a tutorial example script on the 'Error' built-in object type, which is used to create 'Error' objects for runtime exception handling.

The "Error" object type is a built-in object type to be used to create a "Error" object, representing a runtime exception. It has the following main features:

Here is a tutorial example script showing some of the those features:

// Error_Object_Type.js
// Copyright (c) 2013 by Dr. Herong Yang, herongyang.com

   // Creating a new Error object
   var myObject = new Error("Too many users on herongyang.com");

   // Checking this object
   println("\nAbout this \"myObject\":");
   println("   Type = "+(typeof myObject));
   println("   Instance Of Object: "+(myObject instanceof Object));
   println("   Instance Of Error: "+(myObject instanceof Error));

   // Throw my dummy error and catch it
   try {
      // If # sessions on site > 100
      throw myObject;
   } catch (myError) {
      println("\nAbout this \"myError\":");
      println("   Type = "+(typeof myError));
      println("   Instance Of Error: "+(myError instanceof Error));
      println("   myError.name: "+myError.name);
      println("   myError.message: "+myError.message);
   }

   // Catch a real error
   try {
      var o = null;
      o.toString();
   } catch (realError) {
      println("\nAbout this \"realError\":");
      println("   Type = "+(typeof realError));
      println("   Instance Of Error: "+(realError instanceof Error));
      println("   realError.name: "+realError.name);
      println("   realError.message: "+realError.message);
   }

If you run this script with "jrunscript", you will get:

About this "myObject":
   Type = object
   Instance Of Object: true
   Instance Of Error: true

About this "myError":
   Type = object
   Instance Of Error: true
   myError.name: Error
   myError.message: Too many users on herongyang.com

About this "realError":
   Type = object
   Instance Of Error: true
   realError.name: TypeError
   realError.message: Cannot call method "toString" of null

Now we know how to create "Error" objects with the "Error()" constructor.

Read other "Error" related chapters to see more tutorial examples.

Table of Contents

 About This Book

 Introduction to JavaScript

 ECMAScript Language Specification and JavaScript Dialects

 Data Types, Variables and Expressions

 Flow Control Statements

 Creating, Accessing, and Manipulating Arrays

 Defining and Calling Functions

 Web Browser Supporting JavaScript

 Server-Side and Client-Side Web Scripting

 Introduction to Objects

 Defining Your Own Object Types

 Inheritance of Properties and Methods through the Prototype Object Chain

 'jrunscript' - JavaScript Shell Command from JDK

 Using Functions as "Function" Objects

Introduction to Built-in Object Types

 Overview of Built-in Object Types

 The "Object" Object Type - The Root Object Type

 The "Global" Object Type - The Invisible Global Container

 Global Properties and Functions Defined in ECMAScript

 Global Properties and Functions Provided by "jrunscript"

 The "Function" Object Type - Functions Are Objects

 The "Array" Object Type - Arrays Are Objects

 The "String" Object Type - Not Equal to String Primitive Type

 The "Boolean" Object Type - Wrapping Boolean Values into Objects

 The "Number" Object Type - Not Equal to Number Primitive Type

 The "Date" Object Type - Managing Dates and Times

 The "RegExp" Object Type - Regular Expression Patterns

The "Error" Object Type - Runtime Exceptions

 The "Math" Object Type - The Math Container

 W3C's Document Object Model (DOM) Specifications

 References

 PDF Printing Version