Operators
Arithmetic, assignment, comparison and logical operators, plus a few JavaScript surprises.
Operators work on values to produce new values. Most of JavaScript's operators behave as you would expect, but the language's automatic type conversion leads to a few surprises worth knowing.
Arithmetic
JavaScript
const a = 17;
const b = 5;
console.log(a + b, a - b, a * b);
console.log(a / b); // always a decimal division
console.log(a % b); // remainder
console.log(a ** 2); // power
console.log(Math.floor(a / b));Output
22 12 85 3.4 2 289 3
There is only one number type, so 17 / 5 gives 3.4. Use Math.floor or Math.trunc when you want a whole number.
Assignment shortcuts
JavaScript
let score = 10;
score += 5;
score *= 2;
score -= 4;
score++;
console.log(score);Output
27
+ with strings
When either side of + is a string, JavaScript joins instead of adding. The other operators convert strings to numbers.
JavaScript
console.log(1 + 2);
console.log("1" + 2);
console.log(1 + 2 + "3");
console.log("10" - 4);
console.log("5" * "2");
console.log(Number("42") + 1);Output
3 12 33 6 10 43
Logical operators
&&, || and ! work on booleans, but && and || actually return one of their operands. That makes || and the newer ?? handy for default values.
JavaScript
const isMember = true;
const cartTotal = 1200;
console.log(isMember && cartTotal > 1000);
console.log(!isMember);
const nickname = "";
console.log(nickname || "Guest"); // "" is falsy, so we get the default
console.log(nickname ?? "Guest"); // ?? only replaces null and undefined
console.log(null ?? "Guest");Output
true false Guest Guest
The empty line in the output is the empty string nickname, printed by the ?? line.