Sometimes I look online for code and when I find it I realize that I should have known how to do it. Then I feel silly. This is a time when that happened.
I needed to auto-highlight the contents of a read-only textbox or textarea when the user clicked on the input. Easiest javascript I’ve implemented today!
<input type="text" name="textbox" value="Test" onclick="this.select()" />
Amy's Tech Notes 