Updating a contenteditable w/ on:input function is prepending, not replacing, if initial value is empty

[noahlh]

Describe the bug
Sorry for the mouthful of a title. Showing is often easier than telling:

https://svelte.dev/repl/04d08576e3db43d6a7f5c3fd7ae593a3?version=3.23.2

If the initial value is empty, typing into the contenteditable div causes the value to be prepended with the previous value after each keystroke (instead of replaced). Eg typing "Hello" nets a value of:

HelloHelloHellHelHeH

This does not happen if a) the initial value of the field is non-empty or b) after you complete that initial input, you select all the garbage text, delete it, and re-enter new text.

Expected behavior
The value of the element's innerText should reflect exactly what is typed.

Information about your Svelte project:

• Chrome 81 & Safari 13.1.1
• MacOS 10.15.5
• Svelte 3.23.2

Severity
Annoying / semi-blocking (I can work around this in my project, but it does prevent me from initializing the div with an empty value, which I'd prefer)

Additional context
Checked with #support on Discord and was suggested that I file a bug. I searched and couldn't find any related issues. Apologies in advance if this is my mistake and not actually a bug!

[skippednote]

@noahlh You can use binding bind:textContent={text} instead of placing the content within the element.
https://svelte.dev/repl/a3c3b7e51b2647f3b8aebef533e93321?version=3.23.2

However, this does seem to be a bug to me. I'm looking into it.

[skippednote]

I'm getting positive results if we check for the wholeText property on the childNode instead of data.

Swapping the following

export function set_data(text, data) {
	data = '' + data;
	if (text.data !== data) text.data = data;
}

with the this

export function set_data(text, data) {
	data = '' + data;
	if (text.wholeText !== data) text.data = data;
}

https://github.com/sveltejs/svelte/blob/master/src/runtime/internal/dom.ts#L196

[noahlh]

@skippednote Awesome!! Thanks for the quick ID & fix on this.

I did originally use the 2-way binding (which indeed works perfectly), but unfortunately for my application I need to do manual binding, since contenteditable gets set dynamically based on component state, and Svelte doesn't support 2-way binding w/ a dynamic attribute on contenteditable.

[Conduitry]

This is fixed in 3.24.0 - https://svelte.dev/repl/04d08576e3db43d6a7f5c3fd7ae593a3?version=3.24.0

[noahlh]

@Conduitry @skippednote Sorry to be difficult, but I think this might not quite be fixed -- check out the REPL link above, but start typing and hit "enter" in the field. Same issue reappears :(

[skippednote]

@noahlh The URL you had shared earlier uses an older version of Svelte

Try this https://svelte.dev/repl/04d08576e3db43d6a7f5c3fd7ae593a3?version=3.24.0

[noahlh]

@skippednote Sorry - i wasn't clear. I was indeed referring to the link that Conduitry shared (same as yours). The issue appears resolved IF you only type text. But try typing some text then hitting Enter (eg putting in a line break).

[RaiVaibhav]

Hey @noahlh
The reason why content editable worked when clear the input is because mustache tag which is actually a Text node exits inside the editable div, so on clear it gets removed from the editable div, after that there wasn't any text node (which is binded with the state value) and why replication of value happening on pressing next line or enter because {text} (or say Text node) already exits inside the editable div and when we enter something like a\na\na we set this directly to the data of Text node but instead it should be innerText. (this part need the fix in svelte code)

I will definitely say no to the using contenteditable case with a mustache as a child element, it will always create confusion everywhere for cases like <div contenteditable=true on:input={handleInput}>{text}<b>some</b></div> and begineers who is dealing with will have a lot of confusion till then they go through the mdn docs, I think svelte needs to add a warning or info to avoid these cases.

I will open the PR soon for review