Can the data in the stack be modified? For example, can numerical data be modified?

<code>var str = "abc";
str[0]; // "a"
str[0] = "d";
str; //仍然是"abc"</code>

The string is immutable so it cannot be modified

Then can the data in the stack be modified?
For example, num=10;num=11;
What is changed is the value 10 in the stack is changed to 11,
or a new num=11 is created in the stack and the original memory is What about deletion?