Get element by id returns null

Question

The issue is the following:

I have an array with string-type coordinates (‘1_1’) for example, from 0_0 to 3_3 if want to get the element by the id contained in the array it returns null, the array is not null, also if i write the coordinate statically it works.
i added the Ids with innerHTML because i have to create the table depending on the rows and colums selected.
(Dom is loaded)

Check the following to visual support

https://drive.google.com/drive/folders/1-4CIk1LYCay6Q8rA0rLds1JcovdBDf3K

Answer 1

Try to check sequence[0] value

console.log(sequence[0]);
console.assert(sequence [0]==='0_0', "sequence [0] is not equal to '0_0'");