Boolean() casting function

Boolean() casting function converts a value into its boolean equivalent. The following table lists the outcomes of Boolean() casting function:

Data Type	True	False
Boolean	true	false
String	nonempty string	empty string("")
Number	nonzero number and infinity	0, NaN(NotANumber)
Object	Any object	null
undefined	N/A	Undefined

The following code converts a nonempty string to Boolean type:

 
<!DOCTYPE html>
<html>
<head>
    <title>Boolean Example</title>
    <script type="text/javascript">
          
        var aString = "Hello world!";
        var aBoolean = Boolean(aString);
        
        document.writeln(aBoolean); //true
    </script>
</head>
<body>
  
</body>
</html>

Click to view the demo

The following code converts a zero value to Boolean type:

 
<!DOCTYPE html>
<html>
<head>
    <title>Boolean Example</title>
    <script type="text/javascript">
          
        var anInt = 0;
        var aBoolean = Boolean(anInt);
        
        document.writeln(aBoolean); //false
 
              
    </script>

</head>
<body>
  
</body>
</html>

Click to view the demo

Some statment, such as the if statement, automatically perform this Boolean conversion:

 
<!DOCTYPE html>
<html>
<head>
    <title>Boolean Example</title>
    <script type="text/javascript">
          
        var aString = "Hello world!"; 
        
        if (aString){ 
           document.writeln("value is true"); 
        }

        aString = "";
        if (aString){ 
           document.writeln("value is true"); 
        }else{
           document.writeln("value is false"); 
        }
 
        aString = null;
        if (aString){ 
           document.writeln("value is true"); 
        }else{
           document.writeln("value is false"); 
        }
   
              
    </script>

</head>
<body>
  
</body>
</html>

Click to view the demo