JavaScript Variables - Learn Online

Introduction to JavaScript Variables

Lesson Details:
October 21, 2020

I: Introduction

A: Web Development is the task of designing, creating, and updating websites. A web developer’s main concern is with the client-side development of websites, where client refers to the end user’s computer or mobile device. Client-side development includes both front-end development, involving the design of the site’s presentation using HTML, CSS, JavaScript, etc. and Back-end development, which involves the site’s server-side functionality, such as the database.

B: Today, there are many different types of clients that can run a website. Web 2.0 is a term used to refer to websites that allow users to interact and collaborate with each other in a social media dialogue as creators of user-generated content in contrast to websites where users are limited to the passive viewing of content.

II: Body

A: Introduction to javascript variables

JavaScript variables are containers for storing data. They come in 3 types: String, number and object. Strings contain text; numbers contain numerical values; and objects hold collections (arrays) of other objects (numbers, strings, or other objects).


Strings are continuous sequences of characters surrounded by either single or double quotes. Single quotes are used for one-line strings and double quotes for multi-line strings.

var myName = “John”; //single quote var myName = “John Smith”; //double quotes


Numbers can be represented in several ways. The general form is:

var myNumber = 12345; //decimal number var myNumber = .12345; //decimal number var myNumber = 1234.56; //decimal number var myNumber = 1234e-2; //exponential notation var myNumber = 1e4; //exponential notation var myNumber = 0x1234; //hexadecimal notation var myNumber = 0b101010; //binary notation var myNumber = 1e+1; //scientific notation var myNumber = 1e-1; //turn off scientific notation var myNumber = 1000; //in 1000 it will convert from 1000 to 1k


Object properties can be accessed much like object members in C#. The property name is specified in the dot operator (.) followed by a pair of parentheses containing the value assigned to the property. The property name must begin with a letter or underscore and may contain alphanumeric characters plus dollar sign ($) or underscore (_). The value may be a string, a number, a Boolean true/false value, a null value (nothing), a function, an array, or another object.

var personName = { firstName: “John”, lastName: “Smith” }; alert(personName); //The following would be invalid because `john` is not a valid identifier var personName = {‘firstName’: ‘John’}; alert(personName); //is equivalent to alert(personName.firstName); alert(personName.lastName); //is equivalent to alert(personName[‘lastName’]); alert(personName[‘firstName’]); //is equivalent to alert(personName[‘firstName’] ); alert(personName[‘lastName’]); //is equivalent to alert(personName[‘lastName’] ); alert(personName[0]); //is equivalent to alert(personName[‘firstName’]); //note that `firstName` is at index 0 var personPhone = { homePhone: { areaCode: 415 }, workPhone: { areaCode: 650 } }; alert(personPhone); alert(personPhone.homePhone); alert(personPhone.workPhone); alert(personPhone.homePhone.areaCode); alert(personPhone.homePhone.areaCode);

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