What Happens After You Type in URL

Author: Doe Hoon LEE

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Have you wondered what happens after you type in a URL in a browser?

This is one of the mostly asked question in an interview too!

[STEP] 1. We type in a URL !

* DNS (Domain Name System) converts domain name into IP addresses so that computers can understand.

* If addresses were all in numbers (IP addresses), we wouldn't be able to recognize or remember them well.

and this is what #2 is for

[STEP] 2. Browser looks for IP address through DNS

Once the IP address is confirmed, we start communication now!

To access the web server, we need IP and port(80)

[STEP] 3. HTTP request to the server

* The request is made with the following methods so that we know what it is for
    * GET
    * POST
    * PUT
    * HEAD
    * PATCH
    * DELETE
    * *difference between PATCH and PUT
        * PATCH is used when specific/some part is modified only
        * PUT is used when the whole part needs to be updated

[STEP] 4. HTTP response

* HTTP response contains
    * status line
        * 1xx - Informational
        * 2xx - Success
        * 3xx - Redirection
        * 4xx - Client Error
        * 5xx - Server Error
    * HTTP headers
    * message body

[STEP] 5. Browsers begins building DOM.

* HTML parsing
* when it reaches link/script tag, it stops HTML parsing and starts CSS parsing or images or reads JS code
* then when it is done, it goes back to HTML parsing

* in DOM, every entity is considered as node
    * head, body, title, h1, etc. and even attributes and properties are nodes.