1968623 - Testcase inserting N "\n" is 1.8x slower in Firefox (time spent in comparing new value and old value which is required for dispatching change event)

Status: NEW

(Core :: DOM: Core & HTML, defect)

Description

[Mayank Bansal]

Attachment: Insert empty newline.HTML

Open testcase
"Number of empty strings" = 500000
Click on "Insert empty strings"

N=500k
Firefox Samply: https://share.firefox.dev/4jnh4LY (210s)
Chrome: https://share.firefox.dev/43tws3y (117s)
Firefox gecko profiler for 50k: https://share.firefox.dev/3Z2ul5u

Maybe something to improve?

Comment 1

[Masayuki Nakano [:masayuki] (he/him)(JST, +0900)]

Looks like that it takes a little bit long at comparing new value and old value which is required for dispatching change event later. We've already optimized a lot in the editor module about setting the value around ver. 57. I don't think we can optimize this more in the editor module level.

Comment 2

[Mayank Bansal]

Putting this into the general perf component.

Comment 3

[BugBot [:suhaib / :marco]]

The severity field is not set for this bug.
:bas.schouten, could you have a look please?

For more information, please visit BugBot documentation.

Comment 4

[Bas Schouten (:bas.schouten)]

Editor still feels like the right component to me.

Is there an example of a user facing issue resulting from this slowness? If there is please let me know so I can calculate the performance impact, and reset the performance impact flag to request re-triage.

Comment 5

[Masayuki Nakano [:masayuki] (he/him)(JST, +0900)]

No, at least there is no bottleneck in the editor module according to the profile.

• https://searchfox.org/mozilla-central/rev/5e24bf00212b4f5c053c1f8d943becf1b5bfd53c/dom/html/HTMLTextAreaElement.cpp#268
• https://searchfox.org/mozilla-central/rev/5e24bf00212b4f5c053c1f8d943becf1b5bfd53c/dom/base/nsContentUtils.cpp#7684

These are in the DOM module, the former is required to consider whether we should dispatch change event later and the latter is required to sanitize CRLFs. So, I don't have ideas to improve there in the DOM module.

Comment 6

[Masayuki Nakano [:masayuki] (he/him)(JST, +0900)]

FYI: Chrome also converts CRLFs to LFs.

data:text/html,<textarea></textarea><script>const textarea = document.querySelector("textarea"); textarea.value = "abc\r\ndef"; alert(textarea.value.replaceAll("\r\n", "CRLF"));</script>

shows:

abc
def

rather than

abcCRLFdef