Have you ever thought about what happens when you surf the web and have to wait on a webpage to open? It's not as simple as it seems. Yes, there are thousands of websites out there that look like they were developed by a barrel full of color blind monkeys. They are slow just because they were developed like a 2nd grader's papier mâché project. Others think their computer is broken or just blame their spouse. However, people really don't know what happens when you hit GO after typing in www.shopbop.com. Below is a step by step explanation of how a webpage is rendered into a browser.
1.
You type a URL into the address bar of your preferred browser.
2.
The browser parses the URL to find the protocol, host, port, and path.
3.
It forms an HTTP request (that was most likely the protocol).
4.
To reach the host, it first needs to translate the human readable host into an IP number, and it does this by performing a DNS lookup on the host.
5.
Then a socket needs to be opened from the user's computer to that IP number, on the port specified (most often port 80).
6.
When a connection is open, the HTTP request is sent to the host.
7.
The host forwards the request to the server software (most often Apache) configured to listen on the specified port.
8.
The server inspects the request (most often only the path), and launches the server plug-in needed to handle the request (corresponding to the server language you use, PHP, Java, .NET, Python, etc.).
9.
The plug-in accesses the full request, and starts to prepare an HTTP response.
10.
To construct the response a database is (most likely) accessed. A database search is made based on parameters in the path (or data) of the request.
11.
Data from the database, together with other information the plug-in decides to add, is combined into a long string of text (probably HTML).
12.
The plug-in combines that data with some meta data (in the form of HTTP headers), and sends the HTTP response back to the browser.
13.
The browser receives the response, and parses the HTML (which with 95% probability is broken) in the response.
14.
A DOM tree is built out of the broken HTML.
15.
New requests are made to the server for each new resource that is found in the HTML source (typically images, style sheets, and JavaScript files). Go back to step 3 and repeat for each resource.
16.
Style sheets are parsed and the rendering information in each gets attached to the matching node in the DOM tree.
17.
JavaScript is parsed and executed, DOM nodes are moved, and style information is updated accordingly.
18. The browser renders the page on the screen according to the DOM tree and the style information for each node.
19.
You see the page on the screen.
20.
You get annoyed because the whole process was too slow.
I, too, get annoyed when the above steps take longer than one tenth of a second. But now at least I have some documentation to look at, while waiting the remaining fractions of a second before the page renders.
For more pointers on this topic, please contact us. We are happy to assist.
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