Hide/Show button and change textarea as readonly

Hi friends,
Most of the webdevelopers faceing the situation like this.Some times we need to make the text area as editable one when they are going to click the button.We can easily make it by using the javascript.Here I am explaining with the check box.When the user going to click the check box its going to be readonl.Because first it is the editable one.You can make it also in reverse.
For that you put readonly as true in HTML and change the readonly as false in javascript.

< !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" > 
< html xmlns="http://www.w3.org/1999/xhtml" > 
< head > 
< meta http-equiv="Content-Type" content="text/html; charset=utf-8" / > 
< title > Untitled Document< /title > 
< /head > 

< body > 
< script type="text/javascript" > 

function blah(bool) {
if(bool) {
document.getElementById("ta").readOnly = true;
document.getElementById('tst').style.visibility = 'visible'
}
else {
document.getElementById("ta").readOnly = false;
}
}

< /script > 

< textarea id="ta"  > < /textarea > 
< input type="checkbox" onclick="blah(this.checked)" / > 
< div id="tst" style="visibility:hidden" > < input type="button" value="save"/ > < /div > 
< /body > 
< /html > 

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