What’s Mean Immutability in javascript

So In Javascript Docs They Said The All Primitives Are Immutable

so my question is
when i write let x = 'foo';
x = 'bar';
is this mean that a foo Is In a spererate memory location
and bar in another memory location and the garbage collection will collect the old one which is foo

or is it just replacing the value of foo to bar in the same memory location which is firstly defined ?