--description--

Increasing or decreasing a number by one is among the most common numerical operations.

So, there are special operators for it:

• Increment ++ increases a variable by 1:

let counter = 2;

// works the same as counter = counter + 1, but is shorter
counter++;      

console.log(counter); // 3

• Decrement -- decreases a variable by 1:

let counter = 2;

// works the same as counter = counter - 1, but is shorter
counter--;

console.log(counter); // 1

The operators ++ and -- can be placed either before or after a variable.

• When the operator goes after the variable, it is in "postfix form": counter++.

• The "prefix form" is when the operator goes before the variable: ++counter.

Both of these statements do the same thing: increase counter by 1.

Is there any difference? Yes, but you can only see it if you use the returned value of ++/-- .

Let’s clarify. As you know, all operators return a value. Increment/decrement is no exception. The prefix form returns the new value while the postfix form returns the old value (prior to increment/decrement).

To see the difference, here’s an example:

let counter = 1;
let a = ++counter; // (*)

console.log(a); // 2

To summarize:

• If the result of increment/decrement is not used, there is no difference in which form to use:

let counter = 0;
counter++;
++counter;

console.log( counter ); // 2, the lines above did the same

• If you’d like to increase a value and immediately use the result of the operator, you need the prefix form:

let counter = 0;
console.log( ++counter ); // 1

• If you’d like to increment a value but use its previous value, you need the postfix form:

let counter = 0;
console.log( counter++ ); // 0

--questions--

--text--

What are the outputs of the two console.log statements in the JavaScript code below?

let counter = 1;
console.log(2 * ++counter); // Statement A

let counter = 1;
console.log(2 * counter++); // Statement B

--answers--

There is no difference; both console.log statements will show the same result.

Statement A will log 4 because ++counter increments the value before the multiplication. Statement B will log 2 because counter++ increments the value after the multiplication.

Statement A will log 2 because ++counter is a syntax error. Statement B will log 4 because counter++ is the correct way to increment a counter.

Both statements will log 3 because the counter is incremented in both cases before the console.log.

--video-solution--

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