You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
60 lines
3.7 KiB
60 lines
3.7 KiB
Browser
|
|
==
|
|
|
|
## Glossary
|
|
|
|
- **BOM** - The Browser Object Model (BOM) is a browser-specific convention referring to all the objects exposed by the web browser. The `window` object is one of them.
|
|
- **CSSOM** - CSS Object Model.
|
|
- **DOM** - The Document Object Model (DOM) is a cross-platform and language-independent convention for representing and interacting with objects in HTML, XHTML, and XML documents.
|
|
- **Reflow** - When the changes affect document contents or structure, or element position, a reflow (or relayout) happens.
|
|
- **Repaint** - When changing element styles which don't affect the element's position on a page (such as `background-color`, `border-color`, `visibility`), the browser just repaints the element again with the new styles applied (that means a "repaint" or "restyle" is happening).
|
|
- **Composite** - TODO
|
|
|
|
## Rendering
|
|
|
|
High level flow of how browsers render a webpage:
|
|
|
|
1. DOM
|
|
- The DOM (Document Object Model) is formed from the HTML that is received from a server.
|
|
- Characters -> Tokens -> Nodes -> DOM.
|
|
- DOM construction is incremental.
|
|
- CSS and JS are requested as the respective `<link>` and `<script>` tags are encountered.
|
|
1. CSSOM
|
|
- Styles are loaded and parsed, forming the CSSOM (CSS Object Model).
|
|
- Characters -> Tokens -> Nodes -> CSSOM.
|
|
- CSSOM construction is not incremental.
|
|
- Browser blocks page rendering until it receives and processes all the CSS.
|
|
- CSS is render blocking.
|
|
1. Render Tree
|
|
- On top of DOM and CSSOM, a render tree is created, which is a set of objects to be rendered. Render tree reflects the DOM structure except for invisible elements (like the <head> tag or elements that have `display: none`; set). Each text string is represented in the rendering tree as a separate renderer. Each of the rendering objects contains its corresponding DOM object (or a text block) plus the calculated styles. In other words, the render tree describes the visual representation of a DOM.
|
|
1. Layout
|
|
- For each render tree element, its coordinates are calculated, which is called "layout". Browsers use a flow method which only required one pass to layout all the elements (tables require more than one pass).
|
|
1. Painting
|
|
- Finally, this gets actually displayed in a browser window, a process called "painting".
|
|
|
|
###### References
|
|
|
|
- https://www.html5rocks.com/en/tutorials/internals/howbrowserswork/webkitflow.png
|
|
- https://medium.freecodecamp.org/its-not-dark-magic-pulling-back-the-curtains-from-your-stylesheets-c8d677fa21b2
|
|
|
|
## Repaint
|
|
|
|
When changing element styles which don't affect the element's position on a page (such as `background-color`, `border-color`, `visibility`), the browser just repaints the element again with the new styles applied (that means a "repaint" or "restyle" is happening).
|
|
|
|
## Reflow
|
|
|
|
When the changes affect document contents or structure, or element position, a reflow (or relayout) happens. These changes are usually triggered by:
|
|
- DOM manipulation (element addition, deletion, altering, or changing element order)
|
|
- Contents changes, including text changes in form fields
|
|
- Calculation or altering of CSS properties
|
|
- Adding or removing style sheets
|
|
- Changing the "class" attribute
|
|
- Browser window manipulation (resizing, scrolling); Pseudo-class activation (`:hover`)
|
|
|
|
#### References
|
|
|
|
- [How Browsers Work](https://www.html5rocks.com/en/tutorials/internals/howbrowserswork/)
|
|
- [What Every Frontend Developer Should Know About Webpage Rendering](http://frontendbabel.info/articles/webpage-rendering-101/)
|
|
- [Rendering: repaint, reflow/relayout, restyle](http://www.phpied.com/rendering-repaint-reflowrelayout-restyle/)
|
|
- [Building the DOM faster: speculative parsing, async, defer and preload](https://hacks.mozilla.org/2017/09/building-the-dom-faster-speculative-parsing-async-defer-and-preload/)
|