So when I'm trying to add two classes to my elemeny by this code
I have this error
Uncaught DOMException: Failed to execute 'add' on 'DOMTokenList': The token provided ('1 cell-red') contains HTML space characters, which are not valid in tokens.
I don't see any incorrect white space in here
What seems to be the issue is that curr_class is a string containing a space
According to the doc https://developer.mozilla.org/en-US/docs/Web/API/DOMTokenList
You should add the class one by one.
Note also that what your code does is : it takes the class of an element and adds it to the same element so nothing usefull
It seems like you have a space in your class name: 1 cell-red between 1 and cell-red.
One solution would be to add the classes one by one:
myElement.classList.add('1');
myElement.classList.add('cell-red');