How to use AND, NOT and OR Logical Operators in JavaScript

John on September 08, 2020

In JavaScript, we can evaluate the results from multiple comparison statements using the AND, NOT and OR logical operators. These operators will allow us to use as many value comparisons as needed inside a single statement, making the code more efficient.

In this tutorial, we will learn how to use the AND, OR and NOT operators in conjunction with the outcomes value comparisons.

Logical OR Operator

In JavaScript, the OR operator is || (two pipes). Let's say we needed to check if at least one of two comparisons returns true. We could do this by putting an OR operator between them.

var result = 1 > 2 || 1 < 2;

console.log(result);

true

In the above example, we asking is 1 greater than 2 or is 1 less than 2. The first statement is false and the second is true so the result variable is true.

You can chain as many OR statements together as you need and as long as one of the comparisons is true you will get a true result back.

var result = 2 > 4 || 2 > 3 || 1 > 2 || 2 > 1;

console.log(result);

true

2 is greater than 1 so the result variable is true.

Logical AND Operator

The JavaScript AND operator is && (two ampersands). The AND operator is used to check if all comparisons return true.

var result = 2 > 1 && 1 > 1;

console.log(result);

false

2 is greater than 1 and 1 is not greater than 1 so the result variable is false. 

Logical NOT Operator

The JavaScript NOT operator is an ! (exclamation mark). It is used to flip the logical true or false state of a result. Let's demonstrate how this works with an example.

var check = 1 == 1 || 2 == 2;

if (!check) {
 console.log('run code here');  
}

The value of the check variable is true and inside the if statement we are flipping true to false using !. So the code in the if statement will only run if the value of check is false.

Double Negative (!!) NOT Operator

The double not operator is !! (two exclamation marks) and will convert falsy or truthy values into boolean values.

console.log(!!false);

false

console.log(!!0);

false

console.log(!!"false");

true

Conclusion

You now know how to perform multiple comparisons at once and when the OR or AND operators should be used. You also know that the NOT operator can flip a truthy or falsy result and a double negative will create a boolean value from a result.