Shorter Notation

In loops, you change variables all the time, usually by adding or subtracting something. Writing number = number + 1 over and over gets tiring, so JavaScript has shorter ways to write it:

• score += 5; means the same as score = score + 5;
• score -= 5; means the same as score = score - 5;
• score++; means the same as score = score + 1;
• score--; means the same as score = score - 1;

Read += as “add to”: score += 5 means “add 5 to score”. The operators ++ and -- are for the most common change of all: one more, or one less.

let score = 10;
score += 5;
console.log(score);
score -= 3;
console.log(score);
score++;
console.log(score);
score--;
console.log(score);

This prints:

15
12
13
12

The += operator works with text too. It adds text to the end of the variable:

let message = "Hello";
message += ", world";
message += "!";
console.log(message);

Hello, world!

With ++, the loop from the previous exercise gets a little shorter. This is how you will see it written most often:

let number = 1;
while (number <= 3) {
    console.log(number);
    number++;
}

1
2
3

Two typical mistakes:

• score + 5; on its own does nothing. It calculates the result but doesn't store it anywhere, so score doesn't change. You need score += 5;.
• score =+ 5;, with the two characters swapped, doesn't cause an error. JavaScript reads it as score = +5; and simply stores 5 in score. The equals sign always comes second: +=, -=.

All these shortcuts change the variable, so they only work with let. With const, they end with TypeError: Assignment to constant variable.