JavaScript Assignment Operators

The basic assignment operator is =. It stores the value on the right in the variable on the left.

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let total = 10;
total = total + 5;
console.log(total); // → 15

Updating a variable based on its own value is so common that JavaScript has shortcuts.

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let score = 10;
score += 5;   // 15
score *= 2;   // 30
score -= 8;   // 22
console.log(score); // → 22

+= works on strings too, which is handy for building text.

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

Logical assignment

Modern JavaScript adds three more: ||=, &&= and ??=. They assign only when a condition is met. You will meet them in Logical Assignment and Other Modern Operators.

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let name = null;
name ??= "Guest";   // assign only if name is null or undefined
console.log(name);  // → Guest

Assignment is an expression

a = b = 5 assigns 5 to both. It works, but code that does too much on one line is harder to read, so use it sparingly.