In JavaScript, logical operators are used to combine or modify Boolean values. There are three logical operators in JavaScript:
&&: Logical AND operator||: Logical OR operator!: Logical NOT operatorThe logical AND (&&) operator returns true if both operands are true, and false otherwise. Here is an example:
let a = true;
let b = false;
console.log(a && b); // false
console.log(a && true); // true
In this example, the && operator is used to combine two
Boolean values (a and b). The result is false, since b is false.
The logical OR (||) operator returns true if at least one operand is true, and false otherwise. Here is an example:
let a = true;
let b = false;
console.log(a || b); // true
console.log(a || true); // true
console.log(b || false); // false
In this example, the || operator is used to combine two
Boolean values (a and b). The result is true, since a is true.
The logical NOT (!) operator is used to invert the value of a Boolean expression. It returns true if the expression is false, and false if the expression is true. Here is an example:
let a = true; console.log(!a); // false console.log(!false); // true
In this example, the ! operator is used to invert the value
of the a variable, which is true. The result is false.
Logical operators are often used in conditional statements to create more complex conditions. For example:
let a = 5;
let b = 10;
if (a > 0 && b < 20) {
console.log("a is positive and b is less than 20");
}
In this example, the if statement uses the && operator to
create a condition that is true only if both a is greater than 0 and b is
less than 20. If the condition is true, the message "a is positive and b
is less than 20" is logged to the console.
In JavaScript, the double not operator (!!) can be used to convert a non-boolean value to a boolean value. The conversion is based on the "truthyness" or "falsyness" of the value (see truthiness).
Examples:
!!"" // false
!!0 // false
!!null // false
!!undefined // false
!!"Hello" // true
!!1 // true
!!{} // true