Logical Operators

Logical operators in programming refer to symbols that connect two or more expressions in a way where the value returned depends on the original expression and the logical operator used. There are only three logical operators: AND, OR, and NOT.

They have the syntax:

expression OPERATOR expression

Logical AND &&

The logical AND operator returns true when both the expression on the left and right of it are also true. It is symbolised using two ampersands: &&

For Example:

if (10 > 5) && (8 / 2 === 4) {
  alert("Sankara is the greatest programmer that's ever lived");
}

The example above will return true because the expression on the left evaluates to true, and that on the right also evaluates to true. However, if one of them were to return a falsy value, then the entire thing would return false as well. See the example below:

For Example:

if (10 < 5) && (8 / 2 === 4) {
  alert("Sankara is the greatest programmer that's ever lived");
}

This time, the alert will not show because the expression on the right evaluates to false, even though the one on the left is true.

Logical OR ||

The logical OR operator returns true when one or more expressions evaluate to true, and it returns false otherwise. It is represented by two straight slashes: ||.

Using the same example above:

if (10 < 5) || (8 / 2 === 4) {
  alert("Sankara is the greatest programmer that's ever lived");
}

This will show the alert because the right expression is true, and even though the left one is false, the logical OR still evaluates to true.

Logical NOT !

This is used to negate the value of an expression and it is represented by an exclamation mark !. Therefore, you can use it to turn falsy values true, and truthy values false.

For Example:

!false; // will return true
!true; // will return false 
!9 < 5; // returns true

You can combine logical operators into convoluted expressions such as:

if (10 / 2 !== 5) && (30 % 5 === 6) {
  // Do something here
}
 
if ((10 / 2 !== 5) && (30 % 5 === 6)) || ((9 < 5) && (10 > 6)) {
  // Do something here
}

You probably won't need to do this most of the time, however, it's good to know that you can.