How to make buttons select all the text area on the blog

Button select all existing text box area on the blog. With the above title you would have no idea of the design features of the above blog. Yes, this is one way that allows visitors to block content or give the command select all or highlight all with a button. So much easier 
visitors to copy the script / writing in a box / form. If you're still curious please see example below; 

Well, what about the example above? I'm sure you already understand. Good straight out, copy-paste script code below and add the widget or posted on your blog posts.

<Div>
<Form name = "copy">
<Div align = "center">
<Input onclick = "javascript: this.form.txt.focus (); this.form.txt.select ();" type = "button" value = "Select All" /> </ div>
<Div align = "center">
</ Div>
<Div align = "center">
<Textarea cols = "55" name = "txt" rows = "100" style = "height: 50px; width: 300px;"wrap = "VIRTUAL"> Enter the script / text you here .. </ textarea> </ div>
</ Form>
</ Div>

For writing or code blue you please replace with text / script you. Good luck..