Enter key down as IME's convert-decision-operation accidentally send to standard input

[Paalon]

Description

We can't use decision-operation （確定）by enter-key on Japanese IME on macOS on Safari or Chrome with macOS standard Japanese IME or Google 日本語入力 (Google Japanese IME) on standard input like Python's input() in code block. There is no problem on Firefox.
Come from https://teratail.com/questions/4d0bm1aqv9tye5 (Japanese, StackOverflow-like site).

The table work or fail on environments

IME	Safari	Chrome	Firefox
macOS Japanese IME	fail	fail	work
Google 日本語入力	fail	fail	work

I only checked for macOS. I don't know there are problems for Windows or Ubuntu etc.

Reproduce

1. Prepare macOS.
2. Install Japanese IME (macOS Japanese IME (preinstalled) or Google 日本語入力)
3. Write the following Python script in the code block:

text = input()
print(text)

4. Run the code block.
5. Input something (e.g. 今日はいい天気です) in Japanese IME and press enter key as convert-decision-operation.
6. Accidentally, the content is send.

Expected behavior

The content is not send, only do convert-decision-operation.

Context

• Operating System and version: macOS Ventura 13.6.7
• Browser and version:
  • Chrome 125.0.6422.142 (not work)
  • Safari 17.5 (18618.2.12.111.5, 18618) (not work)
  • Firefox 126.0 (work well)
• Jupyter Notebook version:

$ jupyter --version
Selected Jupyter core packages...
IPython          : 8.23.0
ipykernel        : 6.29.4
ipywidgets       : not installed
jupyter_client   : 8.6.2
jupyter_core     : 5.7.2
jupyter_server   : 2.14.1
jupyterlab       : 4.2.1
nbclient         : 0.10.0
nbconvert        : 7.16.4
nbformat         : 5.10.4
notebook         : 7.2.0
qtconsole        : not installed
traitlets        : 5.14.3

Information

To use Japanese IME, convert-decision-operation is mandatory.
There is some notes about keydown event handling with Japanese IME:

• ブラウザでIME確定時のEnterキー入力をハンドリングしない

Firefox（68.0.1）とWindowsのGoogle Chromee（75.0.3770.142）では期待通りに動作します。
MacのGoogle Chrome（75.0.3770.142）とSafari（12.1.2）では、日本語を入力するとき、期待通りに動作しません。

The post written 2020 says we need special treatment for macOS + Safari and macOS + Chrome, and don't need for macOS + Firefox and Windows + Chrome. And need to use KeyboardEvent.keyCode or keypress event but both of them are deprecated.

• SafariでIME確定時のEnterを上手く制御できなかった話

This post written in 2023 also uses KeyboardEvent.keyCode as a solution.

Moved from posted at jupyter/notebook#7389.

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