JavaScript/Notes/Debugging
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Tasks Page[edit]
Find a few tasks on the following page: debugging tasks
Error Reporting in IE[edit]
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![edit]
- 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[edit]
Mac: Opera, Chrome, Firefox: Option + command + i.
Chrome: Debugging JavaScript
debugger keyword[edit]
function myFunc(myParam) {
debugger;
var myVar = 1;
function innerFunc() {
}
}
FIXME: Find and fix the bug[edit]
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
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);
}
[edit]
Firefox: File:Debugger.png
Add a Breakpoint[edit]
A breakpoint is an intentional point in a script put in place for debugging purposes. Opera: Firefox: File:Debugger-breakpoint.png
Debugger Keyword Full Example[edit]
Copy'n'paste this example into your text editor, open your browser, and open this file.
<!doctype html>
<head>
<title>Debugger Example</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<h1>Test Debugger</h1>
<p>
When Entering an Execution Context, the Variable Environment is initialized with parameter
variables, Function Declarations, and Variable Statements.
</p>
<pre>
function myFunc(myParam) {
debugger;
var myVar = 1;
function innerFunc() {
}
}
</pre>
<script>
function myFunc(myParam) {
debugger;
var myVar = 1;
function innerFunc() {
}
}
</script>
<p>Open the debugger and then click the button below.</p>
<button onclick="myFunc(7)">myFunc(7)</button>
</body>
</html>