HTML5中的可调节和多行标签

I am trying to write a canvas graph application by using HTML5 and JavaScript. The main element in this app is a box that the user is able to write a long text in it and the size of the box should adjust while writing the text. I realized that the best way is to use the textarea tag while the user wants to write in it and when the user loses the focus(blur event) on the textarea it will change to a label with the same value in the textarea. You can see the related code below:I am trying to write a canvas graph application