NULL and Undefined and == and === difference

NULL and Undefined

In JavaScript, undefined means a variable has been declared but has not yet been assigned a value, such as:

var TestVar;

alert(TestVar); //shows undefined

alert(typeof TestVar); //shows undefined

null is an assignment value. It can be assigned to a variable as a representation of no value:

var TestVar = null;

alert(TestVar); //shows null

alert(typeof TestVar); //shows object

==  and  ===

=== and !== are strict comparison operators:

JavaScript has both strict and type-converting equality comparison. For strict equality the objects being compared must have the same type and:

·         Two strings are strictly equal when they have the same sequence of characters, same length, and same characters in corresponding positions.

·         Two numbers are strictly equal when they are numerically equal (have the same number value). NaN is not equal to anything, including NaN. Positive and negative zeros are equal to one another.

·         Two Boolean operands are strictly equal if both are true or both are false.

·         Two objects are strictly equal if they refer to the same Object.

·         Null and Undefined types are == (but not ===). [I.e. Null==Undefined (but not Null===Undefined)]

<script type="text/javascript" language="javascript">

        function test() {

            var a;

            alert(a);

            var b = null

            alert(b);

            if (a == b) {

                alert('==');

            }

            if (a === b) {

                alert('===');

            }

        }

   

    </script>

Here are some major differences between HTTP and HTTPS:

HTTP	HTTPS
URL begins with “http://”	URL begins with “https://”
It uses port 80 for communication	It uses port 443 for communication
Unsecured	Secured
Operates at Application Layer	Operates at Transport Layer
No encryption	Encryption is present
No certificates required	Certificates required

HTTP vs HTTPS: Similarities and Differences

What is HTTPS?

HTTPS (Hypertext Transfer Protocol over Secure Socket Layer, or HTTP over SSL) is a web protocol developed by Netscape.

One can say: HTTPS = HTTP + SSL

HTTPS uses Secure Socket Layer (SSL) as a sublayer under its regular HTTP application layering.

Need of HTTPS:

Hypertext Transfer Protocol (HTTP) is a protocol for transmitting and receiving information across the Internet. HTTP serves as a request and response procedure that all agents on the Internet follow so that information can be rapidly, easily, and accurately disseminated between servers, which hold information, and clients, who are trying to access it. You normally use HTTP when you are browsing the web, its not secure, so someone can eavesdrop on the conversation between your computer and the web server. In many cases, clients may be exchanging confidential information with a server, which needs to be secured in order to prevent unauthorized access. For this reason, https, or secure http, was developed by Netscape corporation to allow authorization and secured transactions.

Similarity between HTTP and HTTPS:

In many ways, https is identical to http, because it follows the same basic protocols. The http or https client, such as a Web browser, establishes a connection to a server on a standard port. When a server receives a request, it returns a status and a message, which may contain the requested information or indicate an error if part of the process malfunctioned. Both systems use the same Uniform Resource Identifier (URI) scheme, so that resources can be universally identified. Use of https in a URI scheme rather than http indicates that an encrypted connection is desired.

Difference between HTTP and HTTPS:

1. URL begins with “http://" in case of HTTP while the URL begins with “https://” in case of HTTPS.
2. HTTP is unsecured while HTTPS is secured.
3. HTTP uses port 80 for communication while HTTPS uses port 443 for communication.
4. HTTP operates at Application Layer while HTTPS operates at Transport Layer.
5. No encryption is there in HTTP while HTTPS uses encryption.
6. No certificates required in HTTP while certificates required in HTTPS.

How HTTPS works?

For HTTPS connection, public key and signed certificates are required for the server.

When using an https connection, the server responds to the initial connection by offering a list of encryption methods it supports. In response, the client selects a connection method, and the client and server exchange certificates to authenticate their identities. After this is done, both parties exchange the encrypted information after ensuring that both are using the same key, and the connection is closed. In order to host https connections, a server must have a public key certificate, which embeds key information with a verification of the key owner's identity. Most certificates are verified by a third party so that clients are assured that the key is secure.

In other words, we can say, HTTPS works similar to HTTP but SSL adds some spice in it.

HTTP includes the following actions:

1. The browser opens a TCP connection. 
2. The browser sends a HTTP request to the server 
3. The server sends a HTTP response to the browser. 4. The TCP connection is closed.

SSL will include the following actions:

1. Authenticate the server to the client. 
2. Allow the client and server to select the cryptographic algorithms, or ciphers, that they both support. 
3. Optionally authenticate the client to the server. 
4. Use public-key encryption techniques to generate shared secrets. 
5. Establish an encrypted SSL connection.

6. Once the SSL connection is established the usual transfer of HTTP requests will continue.

Where should https be used?

HTTPS should be used in Banking Websites, Payment Gateway, Shopping Websites, Login Pages, Emails (Gmail offers HTTPS by default in Chrome browser) and Corporate Sector Websites. For example:

PayPal: https://www.paypal.com
Google AdSense: https://www.google.com/adsense/

Beware of using Credit Card Numbers on Internet:  If a website ever asks you to enter your credit card information, you should automatically look to see if the web address begins with https://. If it doesn't, there's no way you're going to enter sensitive information like a credit card number!

Browser integration

Most browsers display a warning if they receive an invalid certificate. Older browsers, when connecting to a site with an invalid certificate, would present the user with a dialog box asking if they wanted to continue. Newer browsers display a warning across the entire window. Newer browsers also prominently display the site's security information in the address bar. Extended validation certificates turn the address bar green in newer browsers. Most browsers also display a warning to the user when visiting a site that contains a mixture of encrypted and unencrypted content.