2.1 Game 2302-0310 javascript  (Page 11/11)

Assistance using Google Chrome

You can open the JavaScript console in the Chrome browser by holding down the Ctrl key and the Shift key and pressing the J key. The console will open atthe bottom of the Chrome browser window. You can also close the console with the same keystroke.

The format of the console is a little messy and may be difficult to navigate. However, it can be useful in locating errors if you can navigate it.

An error message in the console

If you open an html file containing a JavaScript error in the browser while the console is open, an error message will appear in the console. For example, Iam looking at such an error as I type this document. It consists of a round red circle with a white x followed by the following text:

"Uncaught SyntaxError: Unexpected number"

The file name and line number

On the far right side of the same line is text that reads junk.html:23. That is the name of the file and the line number in that file containing the error.That text is a hyperlink. If the hyperlink is selected, another part of the console opens showing the offending line of JavaScript code.

The description is unreliable

Also, in this particular case the description of the error isn't very useful in determining the cause of the error although sometimes it may be useful. Myadvice is not to put too much faith in that description. The error was actually a missing relational operator in a comparison clause.

The line number is very important

Probably the most useful information is the line number that you can use to go back and examine your source code, looking for an error in that line of code.

Assistance using Firefox

You can open an error console when using the Firefox browser by holding down the Ctrl key and the Shift key and pressing the J key. The console will open in aseparate window. Unlike with Chrome, repeating the keystroke won't close the error console.

An error message in the console

If you open an html file containing a JavaScript error in the browser while the error console is open, an error message will appear in the console. Forexample, I am looking at such an error as I type this document. It consists of a round red circle with a white x and the following text:

missing ) after condition

file: --html file name and path here-- Line: 23

while(h 0){

The middle line is a hyperlink

The middle line of text that contains the file name to the left of the line number is a hyperlink. If you select the link, a window will open showing thesource code with the problem line highlighted. Pressing the right arrow key will cause a blinking cursor to appear between the first and second characters inthat line.

The description is unreliable

As with Chrome, in this particular case the description of the error isn't very useful in determining the cause of the error although sometimes it may be useful. Myadvice is not to put too much faith in that description. The error was actually a missing relational operator in a comparison clause.

The line number is very important

Probably the most useful information is the line number that you can use to go back and examine your source code, looking for an error in that line of code.

Run the scripts

I encourage you to run the scripts that I have presented in this lesson to confirm that you get the same results. Copy the code for each script into atext file with an extension of html. Then open that file in your browser. Experiment with the code, making changes, and observing the results of your changes. Makecertain that you can explain why your changes behave as they do.

Miscellaneous

This section contains a variety of miscellaneous information.

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