JavaScript/Notes/Debugging: Difference between revisions
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=== FIXME: Find and fix the bug === | |||
The code example below must be changed to output: | |||
<pre> | |||
Check the value of i: 0 | |||
Check the value of i: 1 | |||
Check the value of i: 2 | |||
Check the value of i: 3 | |||
</pre> | |||
<strong>Example</strong> | |||
<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> | |||
=== debugger from the menu === | === debugger from the menu === | ||
Firefox: | |||
[[File:Debugger.png]] | [[File:Debugger.png]] | ||
Revision as of 11:30, 1 January 2014
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
A few approaches:
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
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>