JS: Boolean Operators

Logical-and operator

x && y

• Return true if both Boolean(x) and Boolean(y) are true, else false.
• If Boolean(x) is false, y is not evaluated.

// “and” operator
console.log(true && true);

• JS: Boolean Constructor

Logical-or operator

x || y

• Return true if one of Boolean(x) or Boolean(y) is true, else return false.
• If Boolean(x) is true, y is not evaluated.

// “or” operator
console.log(true || true);

Logical-not operator

!x

• Reverse the boolean value.
• Return true if Boolean(x) is false, return false if Boolean(x) is true.

// “logical negation” operator
console.log(!false);

Operator precendence

precedence from highest to lowest is:

• ! (logical NOT). highest precedence.
• && (logical AND)
• || (logical OR)

!a && b || c
// parsed as: ((!a) && b) || c

and

• ! is right-associative.
• && is left-associative.
• || is left-associative.

a && b && c;
// means
// (a && b) && c

a || b || c;
// means
// (a || b) || c

!!a;
// means
// !(!a)