Logical AND

The logical AND operator is &&.

 
var result = true && false;

Logical AND behaves in the following truth table:

OPERAND 1	OPERAND 2	RESULT
true	true	true
true	false	false
false	true	false
false	false	false

Logical AND can work on any type of operand, not just Boolean values.

When logical AND working with non-Boolean values:

OPERAND 1	OPERAND 2	RESULT
object	any value	return the second operand
and value	object	return the second object if the first operand evaluates to true.
object	object	return the second operand
null	any value	null
any value	null	null
NaN	any value	NaN
any value	NaN	NaN
undefined	any value	undefined
any value	undefined	undefined

Short-circuited operation

The logical AND operator is a short-circuited operation. The short-circuited operation means that if the first operand determines the result, the second operand is not evaluated. For logical AND, if the first operand is false, the second operand is not evaluated since the result is false.

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        var found = false; 
        var i = 1;
        var result = (found && i++); 
        document.writeln(result); //false
        document.writeln(i); //1
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo