If I change a variable’s value will the original value still exist inside the memory?

let a = 7;
a = 3;
console.log(a); // output 3

In this case, the value 7 is still inside a memory? I was reading that all primitive data types are immutable.

Answer

The value of a is kept in memory, until garbage collection eventually recycles it. What the docs mean by immutable is that you can’t directly alter the primative (in this case the integer 7). You can only replace the value.

There are examples on the docs but this is another one

let a = 1;
a.toString() // a is still 1, it cannot be mutated

However, we can assign this to another variable

let a = 1;
let b = a.toString() // b is string "1" and a remains as the integer 1

Or we can replace the value

let a = 1;
a = 10; // a is 10