Logical operators JS Home  <<  JS Reference  <<  Logical

Returns a boolean value where possible or one of the expressions used when not.

Description

Logical operators are generally used in conditional statement to retrieve a true or false value and apply this to the conditional statement in question.

  • Logical operators are evaluated from left to right.

&& - Logical AND

This operator returns true if both its operands can be convered to true otherwise returns false.

  • If the first operand evaluates to false then the operator will 'short circuit' and not test the second operand as both operands have to evaluate to true.

Lets see some examples of using the logical AND operator.


// Store properties in an array.
var andProps = new Array(5);

andProps[0] = false && true; 
andProps[1] = true && false; 
andProps[2] = false && false; 
andProps[3] = true && true; 
andProps[4] = 'a' && 'b'; 

alert(andProps);

Press the button below to action the above code:

|| - Logical OR

This operator returns true if either of its operands can be convered to true otherwise returns false.

  • If the first operand evaluates to true then the operator will 'short circuit' and not test the second operand as only one operand has to evaluate to true.

Lets see some examples of using the logical OR operator.


// Store properties in an array.
var orProps = new Array(5);

orProps[0] = false || true; 
orProps[1] = true || false; 
orProps[2] = false || false; 
orProps[3] = true || true; 
orProps[4] = 'a' || 'b'; 

alert(orProps);

Press the button below to action the above code:

! - Logical NOT

This operator returns true if operand is not true otherwise returns false.

Lets see some examples of using the logical NOT operator.


// Store properties in an array.
var notProps = new Array(3);

notProps[0] = !true; 
notProps[1] = !false; 
notProps[2] = !'a'; 

alert(notProps);

Press the button below to action the above code:

Related Tutorials

JavaScript Intermediate Tutorials - Lesson 3 - Conditional Statements