What does ‘numeric literal’ mean in java script?

Question

I’m building a calculator with java script and getting the following syntax error as I enter a problem of this type: a * b * c

“No Identifiers allowed directly after numeric literal at Line 50.”

In my function, where I solve the mathematical problem, I’m taking the string of an input field where you have to enter your question, replace ‘x’ with ‘*’ (and the division symbol with ‘/‘) and simply use eval() to solve it. However, the error shown above occurs if I try to use the html buttons where you insert the characters into the text. When I press ‘=‘ on e.g. ‘5x9x6’ the error is thrown. However if I switch to the keyboard and enter ‘5*9*6’ everything works perfectly.

Here Is my function:
function calc() {
res = document.getElementById('x').value;
res=res.replace('x', '*');
res=res.replace('÷', '/');
(line 50): document.getElementById('x').value=eval(res);

Here is my code:
https://code.sololearn.com/W4TkgSK7hdX3/?ref=app

Can anyone explain me, what I’m doing wrong? Thanks.