Bug: Unexpected result of adding class when create element

[xiaodong2008]

What is the current behavior?

button class="b t n"

What is the expected behavior?

button class="btn"

Steps to reproduce the problem

• Open playground
• Check element <button>

Link to minimal reproduction

https://stackblitz.com/edit/fastjs-reproduce-n5bqw6?file=src%2Fmain.ts

System Info

No response

Any additional comments?

No response

Confirmations

• [X] I'm using/tried the latest version of fastjs and the bug is still there
• [X] I have read the Code of Conduct
• [X] I have read the Issue Reporting Guidelines
• [X] I have searched for similar issues in both open and closed tickets and cannot find a duplicate
• [X] I know that any inappropriate content may cause the maintainer to take action base on the Code of Conduct