Javascript textarea undo redo

I'm making a small javascript editor (for a chrome extension) somewhat like the one on SO.

There's a toolbar for manipulation of the text in the textarea. (e.g. surround the selected text with some template)

I was wondering if there is a easy way to achieve this, currently when using the system undo/redo, it messes the text up (I think the system is only keeping track of deltas between edits).

Answers:

Answer

You can probably simulate textInput events to manipulate the contents of the textarea. The changes made that way are respected by undo/redo, I think (I know they are in Safari)

var element = document.getElementById('someTextarea');
var text = 'This text will be inserted in the textarea';
var event = document.createEvent('TextEvent');

event.initTextEvent('textInput', true, true, null, text);
element.dispatchEvent(event); // fire the event on the the textarea

Basically, the text is inserted as though you pasted it yourself. So if something is selected, it'll be be replaced with the text. If there's no selection, the text will be inserted at the caret's position. And undo/redo should work normally (undoing/redoing the entire inserted string in one go), because the browser acts as if you typed/pasted it yourself.

As I said, I know this works like a charm with undo/redo in Safari, so I'd assume it works in Chrome as well.

Answer

If the textarea has focus and its caret is at the correct position,

document.execCommand("insertText", false, "the text to insert");

will insert the text "the text to insert", preserving the browser's native undo stack. (See the work in progress HTML Editing API spec.) Chrome 18 supports this, but I'm unsure of the exact version it was introduced.

Answer

Here's a solution which works in Firefox too (but without the undo functionality)

// Solution
function insertText(textarea, text) {
	// https://stackoverflow.com/a/55174550/288906
	if (!document.execCommand('insertText', false, text)) {
		textarea.setRangeText(text);
	}
}

// Demo code to add text on click
const textarea = document.querySelector('textarea');
textarea.onclick = () => insertText(
  textarea,
  '@'
);
<textarea>Click in here to add text</textarea>

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