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The postfix and prefix forms

importance: 5

What are the final values of all variables a, b, c and d after the code below?

let a = 1, b = 1;

let c = ++a; // ?
let d = b++; // ?

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