Tested the issue on chrome reported version 65.0.3325.181 using windows-7 with steps mentioned below:
1) Launched chrome reported version and navigated to URL: https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_onkeyup
2) Tried to replace the data in it with
inputValue = this.value;
newValue = convertKatakanaToRomaji(inputValue);
this.value = newValue; (as provided in comment#0)
3) On output part didn't observed anything related to the issue

@Reporter: Could you please provide sample Test file/URL that reproduces the issue which helps us in further triaging the issue in better way, any inputs from your end are most helpful.

Thanks!

Hi viswa.karala,

Thank you for your reply.

The issue only occur on IME-mode ON. Please input a double byte number(Japanese character) on below URL.
https://www.w3schools.com/code/tryit.asp?filename=FPYBOZ5XOZ8J

Sample Input:
１
１２
１２３
(not copy-paste) 

Problem:
case '１' <-- the underline below 1 still display
case '１２' or '１２３' <-- the previous inputs were not cleared after executing x.value = <newValue> 

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Tested the issue on chrome reported version using Windows-7 with steps mentioned below:
1) Launched chrome reported version and navigated to URL: https://www.w3schools.com/code/tryit.asp?filename=FPYBOZ5XOZ8J
2) Clicked on RUN in the opened URL and Changed the input language source to Japanese, typed '1' in the input field, seen underline for '1' and clicked on enter, then underline disappear
3) Typed '2 3', underline is seen only for '2 & 3', clicked on enter, then underline disappear
4) Again typed '1 2 3', seen underline for '1 2 3' and underline disappear after clicking Enter
Observations: Tested the issue on 64.0.3282.186, seen the same behaviour as mentioned above.

@Reporter: Please find the attached screen cast for your reference and provide your feedback on it. if possible provide the screen cast of the issue which helps us in better understanding, any further inputs on it are most helpful.

Thanks!

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Following the same steps as yours, the result in my case is different.
Please see attached clip.

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Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

mngabutan@ Thanks for the update.

Able to reproduce the issue on Windows 10 and Mac OS 10.13.3 on the latest Canary 67.0.3387.0 and Stable 65.0.3325.181 by following the given steps as per comment #7.
Unable to reproduce this issue on Ubuntu 17.10.

The issue is observed when On-screen keyboard is used and when keypad is used, the issue is not seen.
Attached is the screen cast for reference.

This is a Non-Regression issue as this behaviour is observed from M60 Chrome builds. 
Hence marking this as Untriaged for further updates from Dev.

Thanks..

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viswa.karala@, the reporter didn't mean '1 2 3' (ASCII 1, space, ASCII 2, space, ASCII 3), but meant '１２３' (Three non-ASCII characters; U+FF11 U+FF12 U+FF13).

I reproduced this on Windows 10 with a physical keyboard + Google Japanese Input. Please bisect again with a physical keyboard.

Able to reproduce the issue on Windows 10 and Mac OS 10.13.3 on the latest Canary 67.0.3389.0 and Stable 65.0.3325.181 with a physical keyboard.
Note: unable to reproduce the issue while entering text from Numlock keys
Unable to reproduce this issue on Ubuntu 14.04 and 17.10.

This issue is seen from M60 chrome builds and the same behaviour is observed on M64 - 64.0.3282.186 build and M65 - 65.0.3325.181 build.
Attached is the screen cast of the behaviours of the above versions for reference.

Considering this issue as Non-Regression issue as this is seen from M-60 chrome builds.(We consider M-60 as the base for Non-Regression issue).
Hence removing 'Needs-Bisect' label. Please feel free to add if further bisect is required.

Thanks..

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