en.javascript.info/1-js/02-first-steps/07-operators/1-increment-order/solution.md

The answer is:

• a = 2
• b = 2
• c = 2
• d = 1

let a = 1, b = 1;

alert( ++a ); // 2, prefix form returns the new value
alert( b++ ); // 1, postfix form returns the old value

alert( a ); // 2, incremented once
alert( b ); // 2, incremented once