Errata

There is no longer a Current_Release Anchor on the http://docs.jquery.com/Downloading_jquery page.

The point of the html is that nothing on the page gets rendered until the page's "Alert" on line 8 is responded to. In javascript "alert" is case sensitive. Since "alert" is spelled "Alert" instead of "alert" the browser simply ignores the line and everything gets rendered immediately (there is no "This page says" + Environment.NewLine + "Hello world!").

This might not seem like much but when you are starting out is very confusing and it took me a couple of wasted hours to figure out the problem.

All of the alert calls which are supposed to hold up the rendering of the page until answered are spelled Alert. This function call is case-sensitive and this incorrect spelling causes the Alert to simply be ignored and the page rendered immediately. Doesn't sound like much but when you are new trying to get thing to work it is very frustrating.

The book has the correct typing, but the file that is downloaded references a newer jQuery version.
<script src="../_js/jquery-1.7.2.min.js"></script>
Fatal error when using this extension with the code in the book. To make the code work you need to change the external JavaScript file back to version 1.6.3. Please make this correction on the download link.

For some reason I did not get the expected result here. It was only after comparing the completed version and a few tests removing and adding sections of the complete code to my version did I find that you must also add the 'return false' statement onto line 11 (after declaring the processData function and before the end of the 'submit' function) in order to get the expected result

All of the JSON examples on pages 371-375 are wrong. These are not JSON, they are JavaScript object literals. There's a big difference. In JSON, all strings must be enclosed in double quotes. Neither unquoted identifiers nor single quoted strings will work, only double quotes are acceptable. Test the book code using any JSON validator and you will see that it fails validation. In addition, function processContacts on page 373 will not work because the getJSON call (which should not have a space) will fail silently and not pass the data parameter. If program contacts.php uses the PHP function to generate JSON, it will properly enclose evrything in double quotes. But the var data = { ... } lines in the book are not what PHP returns. -- Jesse Heines, UMass Lowell Dept. of Computer Science, heines@cs.uml.edu

The code example presents the error where a single equals sign is used in an if statement:
if (score=0) {
alert('game over');
}
The text then continues: "However, in this case, the alert message will 'always' display, no matter what value is stored in 'score' prior to the conditional statement."

This is incorrect. In this example, the alert message will never display. The reason is that the value 0 is assigned to the variable 'score', and this value is evaluated by the if statement. Because 0 always evaluates to false, the alert statement does not execute. If the assignment had been "if (score=1)", then the value 1 would have been assigned to the variable score and this would have been evaluated as true and the alert message would have been displayed.

The end of the paragraph states "The JavaScript interpreter treats an assignment operation as 'true'...". This is incorrect. The interpreter treats it as true or false based on the value of what is on the right side of the equals sign.

You can see this by running the code. You will see that the alert statement is not displayed. Then change the if statement to
if (score=1)
and the statement will be displayed.

The solution in the book to this problem is correct: simply replace the single equals sign with a double equals sign. So "if (score=0)" should be replaced by "if (score==0)".

First there is this code listed in pt. 6:
$('.main').html('<p>You have successfully logged on!</p>');

Then there is this in pt. 7:
$('#content').html('<p>You have successfully logged on!</p>');


"#content" should be changed to ".content".

Using jquery-1.11.0 it seems that use of field.attr('defaultValue') causes the code not to run right because defaultValue is returned as "undefined" by attr(), thus field.val() will never match field.attr('defaultValue).

Per jQuery api http://api.jquery.com/attr/, "As of jQuery 1.6, the .attr() method returns undefined for attributes that have not been set. To retrieve and change DOM properties such as the checked, selected, or disabled state of form elements, use the .prop() method."

Changing from attr() to prop() allows example to run. Replace code line 3 with:

if (field.val()==field.prop('defaultValue'))