JavaScript/Notes/Debugging
Tasks Page
Find a few tasks on the following page: debugging tasks
Error Reporting in IE
In IE, go to Tools > Internet Options and choose the Advanced tab. Make sure the check box for "Display a notification for every script error” is checked.
It Doesn't Work!
- Make sure you've correctly added a closing </SCRIPT> tag.
- Check the error console.
- Validate the HTML Markup
- See also Code Guidelines for Rich Internet Application Development
How to Launch the Debugger
Mac: Opera, Chrome, Firefox: Option + command + i.
Chrome: Debugging JavaScript
debugger keyword
<source lang="javascript"> function myFunc(myParam) {
debugger;
var myVar = 1;
function innerFunc() {
}
} </source>
FIXME: Find and fix the bug
The code example below must be changed to output:
Check the value of i: 0 Check the value of i: 1 Check the value of i: 2 Check the value of i: 3
Example <source lang="javascript"> var count = 0; var output = document.getElementById("output");
for ( var i = 0; i < 4; i++ ) {
setTimeout(function(){
output.textContent = "Check the value of i:" + i;
}, 200);
} </source>
Firefox:
Add a Breakpoint
A breakpoint is an intentional point in a script put in place for debugging purposes.
Opera:
Firefox:
Debugger Keyword Full Example
Copy'n'paste this example into your text editor, open your browser, and open this file. <source lang="html5"> <!doctype html> <head> <title>Debugger Example</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body>
Test Debugger
When Entering an Execution Context, the Variable Environment is initialized with parameter variables, Function Declarations, and Variable Statements.
function myFunc(myParam) {
debugger;
var myVar = 1;
function innerFunc() {
}
}
<script> function myFunc(myParam) {
debugger;
var myVar = 1;
function innerFunc() {
}
} </script>
Open the debugger and then click the button below.
<button onclick="myFunc(7)">myFunc(7)</button> </body> </html> </source>