javascript

Chapter 14: Error Handling and Debugging
In IE 8, Firebug, Chrome, and Safari, the message display on the error console differs according to the
method that was used to log the message. Error messages contain a red icon, whereas warnings contain a
yellow icon. Console messages may be used, as in the following function:
function sum(num1, num2){
console.log(“Entering sum(), arguments are “ + num1 + “,” + num2);
console.log(“Before calculation”);
var result = num1 + num2;
console.log(“After calculation”);
}
console.log(“Exiting sum()”);
return result;
As the sum() function is called, several messages are output to the JavaScript console to aid in
debugging. The Safari JavaScript console can be opened via the Develop menu (discussed earlier); the
Chrome JavaScript console is opened by clicking the “ Control this page ” button and selecting Developer
JavaScript console (also discussed earlier); and the Firebug console is accessed by clicking the icon in the
lower - right corner of the Firefox status bar. The IE 8 console is part of the Developer Tools extension,
which is available under the Tools menu; the console is on the Script tab.
Opera ’ s JavaScript console is accessible using the opera.postError() method. This method accepts a
single argument, the message to write to the console, and is used as follows:
function sum(num1, num2){
opera.postError(“Entering sum(), arguments are “ + num1 + “,” + num2);
opera.postError(“Before calculation”);
var result = num1 + num2;
opera.postError(“After calculation”);
}
opera.postError(“Exiting sum()”);
return result;
The opera.postError() method can be used to write out any type of information to the JavaScript
console, despite its name.
Another option is to use LiveConnect, which is the ability to run Java code from JavaScript. Firefox,
Safari, and Opera all support LiveConnect and may interact with a Java console. It ’ s possible to write
messages to the Java console using JavaScript via the following code:
java.lang.System.out.println(“Your message”);
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