Array Length

The number of items in an array is stored in the length property.

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        var colors = ["A", "B", "C"]; //creates an array with three strings 
        var names = [];               //creates an empty array 
        document.writeln(colors.length); //3 
        document.writeln(names.length); //0 
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

length is not read-only.

By setting the length property, you can remove or add items to the end of the array.

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        var colors = ["A", "B", "C"]; //creates an array with three strings 
        colors.length = 2; 
        document.writeln(colors[2]);         //Undefined 
        
        colors[99] = "D";                   //add a color (position 99) 
        document.writeln(colors.length); //100 
        
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

The following code adds item to the end of an array.

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        var colors = ["A", "B", "C"]; //creates an array with three strings 
        colors.length = 4; 
        document.writeln(colors[3]); //Undefined 
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

The following code adds items to the end of an array with the length property:

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        var colors = ["A", "B", "C"]; //creates an array with three strings 
        colors[colors.length] = "D"; //add a color (position 3) 
        colors[colors.length] = "E"; //add another color (position 4) 
        document.writeln(colors[0]); 
        document.writeln(colors[1]); 
        document.writeln(colors[2]); 
        document.writeln(colors[3]); 
        document.writeln(colors[4]); 
        document.writeln(colors[5]); 
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

The last item in an array is always at position length - 1.