Clients

Important Browser functions:

• Render web pages from Responses

• Manage certificates

• Encode messages for HTTPS

• Manage storage spaces and policies

• Work with OS to resolve DNS and cache addresses

Rendering Pipeline:

This is the browsers process of taking an http response, parsing it, building the DOM and then drawing the content to the screen. This is then repeated as the user interacts with the page or/and on a loop based on time. JS can then edit the DOM before the initial drawing to screen or after based on triggering actions. During DOM Tree creation the browser will also make any GET requests needed to grab external content referenced by things such as script, style, image, font, video, and meta tags. The DOM will then be updated by JS as the user interacts with the page or in the background as changes happen. As the DOM is updated the page is also updated without refreshing the who page.

JavaScript and DOM: Often times we want to edit or inject script tags into a page to do our dirty work. When the script tag is loaded into the DOM it will, in-parallel, run the JS. This can cause problems if the DOM is not finished being built and the JS is trying to interact with nodes(elements) that dont yet exist.

Use the defer <script> attribute to avoid running JS before the DOM is complete.

JavaScript and hacking: The Browser Security Model forces JS to run in a sandboxed environment. This model also restricts various JS actions: Start or access processes, read arbitrary system memory, read the systems file system, access the network layer, call OS functions, registering event listeners, directly make http calls as the user, open new web pages, write entries to the browser history, or get location and send notifications without permission.