Please describe the whole process from entering a URL in the browser to rendering the page.

I believe many front-end programmers have encountered this problem during the interview , The first time I encountered this problem, I was ignorant , I was unprepared to talk nonsense , Naturally, the interview is cold , I have learned this piece recently , Make a record here ~

Overall process ：

1. If URL Contains domain names , The browser connects to DNS（ Domain name server ）, Find the domain name IP Address ;
2. web The browser connects to the corresponding web The server , issue http request , What you want ;（TCP Three handshakes ）
3. web The server checks whether the requested resource exists , To be is to return , Returns if it does not exist 404;
4. web The browser receives the resource and closes the connection ;（TCP Four waves ）
5. The browser parses the entire page , And check for other resources needed , Such as the picture ;
6. Keep sending out http request , Request corresponding resources ;
7. All resources requested , The page is completely displayed . 

Key content

DNS：Domain Name Service Domain name service , Resolve the domain name to ip, This process involves CDN, I will learn in detail later CDN.

TCP/IP Overall process of the agreement ：

application layer ： Application specific protocols , Such as WWW、 E-mail 、FTP etc. . 

TCP Transport control layer ：Transmission Control Protocol Transport control layer protocol ,TCP It's connection-oriented , Reliable byte stream transport service .TCP Use the port number to direct packets to a specific application on the computer .

IP The network layer ：Internet Protocol Network layer protocol ,IP It's an unreliable , No connection protocol .IP Pass the packet through IP Address transfer to the specified computer .

Hardware layer ： Convert binary data into photoelectric signals .