jQuery – SelectorGadget and interactive tester

Posted on October 27, 2010 by hedleyproctor

One of the fundamental features of the jQuery javascript library is its powerful selectors, that allow you to find elements in the DOM tree using CSS syntax. However, it can be annoying if you are writing some code and your selectors don’t seem to be picking out the object or objects you want. Did you know that there are some very useful tools to help in this situation:

SelectorGadget is a tool that you can open on any web page. You then select an html element and it writes the CSS selector for you!
http://www.selectorgadget.com/

Alternatively, if you want to interactively test a selector against arbitrary html, try:
http://www.woods.iki.fi/interactive-jquery-tester.html

Posted in jQuery | Tagged , | Leave a comment

varchar and text data types in MySQL

Posted on October 26, 2010 by hedleyproctor

Do you know the difference between the varchar and text types in MySQL? Up until MySQL 5.0.3, the varchar data type could only hold up to 255 characters, but from 5.0.3 onwards, it can store up to 65,535, which means that it can store data that previously would have been held in text fields. This is important because text is a fundamentally different data type to varchar. In fact is is similar to the blob data type, and has a couple of disadvantages:

  1. You can’t make a complete index on a text column, so MySQL will often have to read from the table.
  2. MySQL can’t make temporary tables in memory for tables that use text columns, it has to create temp tables on disc for them.

So most of the time you’ll probably be better off using varchar columns rather than text. For more info, see:

varchar length:
http://dev.mysql.com/doc/refman/5.0/en/char.html

Indexes:
http://forums.mysql.com/read.php?24,105964,105984#msg-105984

How MySQL uses temporary tables:
http://dev.mysql.com/doc/refman/5.0/en/internal-temporary-tables.html

Posted in MySQL | Tagged | Leave a comment