Increment and decrement operations in JavaScript

Consider the following code:

let num = 0;
num = num + 1; // add the number 1 to the variable num
alert(num);    // shows 1

As you already know, this code can be rewritten in an shortened form through the operator +=:

let num = 0;
num += 1;     // add the number 1 to the variable num
alert(num);   // shows 1

In fact, adding one in programming is so common that an even more shortend syntax has been invented for this operation - the special operator increment ++, which increases the value of a variable by 1.

Let's rewrite our code with it:

let num = 0;
num++;        // add the number 1 to the variable num
alert(num);   // shows 1

There is also the operation decrement --, which decreases the value of a variable by 1. See an example:

let num = 0;
num--;        // subtract the number 1 from the variable num
alert(num);   // shows -1

Modify this code such a way that it contains increment and decrement operations:

let num = 10;
num = num + 1;
num = num + 1;
num = num - 1;
alert(num);