The length property

Functions

• What is a function?
• Pre-defined functions
• Scope of Variables
• Function Expressions
• Anonymous Functions
• Callback Functions

Objects

• What is an object?
• Accessing Object Properties
• Calling an Object’s Methods
• Altering Properties/Methods

Array Properties and Methods

• The length property
• Stack Methods
• Queue Methods
• Reordering Methods
• Manipulation Methods
• Location Methods
• Iterative Methods
• Working with array of objects

DOM

• The Document Object Model
• Node Relationships
• Working with the Contents of Elements
• Getting Elements by ID, Tag Name, or Class
• Adding and removing element

Built-in Objects

• Object Types
• The String Object
• The Window Object

Using Events in JavaScript

• What are events?
• Handling events
• DOM manipulation using events

Handling Input and Output

• Understanding HTML Forms
• Working with the Form Object
• Validating user input

Ajax and JSON

• Introduction to AJAX and JSON
• Viewing AJAX in action
• Using the XMLHttpRequest object
• Putting Objects in Motion with JSON

The number of items in an array is stored in the length property, which always returns 0 or more, as shown in the following example:

var colors = ["red", "blue", "green"]; //creates an array with three strings
var names = []; //creates an empty array
alert(colors.length); //3
alert(names.length); //0

Example

Create an array with a few values and print the length of the array in the console.

var people = ['Bob', 'Jack', 'Marcy', 'Wilson'];
console.log(people.length);