JavaScript: Quickly insert text into long textarea

Question

I am playing around with creating an HTML-textarea based plain text editor to edit my scripts (using e.g. Mozilla Prism + a localhost install/ webserver). It works fine so far, but when I want to insert something at the cursor position, it gets slow in Firefox when there is a lot of text in the textarea (Chrome works fine). E.g. with 133k filled in the textarea it takes around 1 sec to perform inserting 4 spaces.

I already have and use elm.selectionStart and elm.selectionEnd. Based on these I then copy the text, manipulate it, and set the value back into the textarea -- perhaps that is what's causing the bottleneck (I'm using the similar approach as answered on this site before). Ideally, I would probably like to have something like elm.selectedText = 'foobar' but can't find this...

It doesn't necessarily need to be crossbrowser...

Can someone help?

Answer 1

According to this article on codemirror, using designMode is faster than using a textarea, because you can edit parts of the content instead of editing the whole text in one go.