current position:Home>Summarize the browser operation mechanism in the simplest words
Summarize the browser operation mechanism in the simplest words
2021-08-26 00:39:02 【JOJO's wonderful front end】
This is my participation 8 The fourth of the yuegengwen challenge 8 God , Check out the activity details :8 Yuegengwen challenge
Rendering process :
- Input url, Browser according to DNS The server gets the domain name IP Address
- Request... From the server , The server returns the request , The client gets the returned content
- Top down generation dom Trees
- Rendering css Trees , Generate cssom
- Rendering layout, Calculate node size , Location
- Render the page according to the above
reflection
During rendering , If you encounter <script>
Stop rendering , perform JS Code , At this time, the parser is in a suspended state , etc. JS After loading , And then build
therefore , It is suggested that script The label on the body label Bottom That's why
structure
dom tree The root of is document, Left branch right pole is head and body, The following are tree leaf nodes
backflow / rearrangement :
When part or all of the rendering tree needs to be rebuilt due to layout problems , It will flow back / rearrangement , Every page must have one , When it was first loaded
Repaint : When a part of the rendering tree needs to be rebuilt due to problems such as style , Will redraw
Rearrangement will definitely redraw , But redrawing does not necessarily rearrange
Rearranging and redrawing will cause the browser to take time , Katon and so on , So don't repeat changes frequently dom
Optimize according to the above problems
- Direct change classname
- If you want to create more than one dom, Just add it all at once
- Elements that require multiple rearrangements , Set absolute positioning away from the document stream , It won't affect other elements
- Avoid using CSS expression
- Avoid using table Layout
So with virtual dom To optimize this
fictitious dom Yes, it is js The simulated tree , Once built, it will be rendered to the document stream at one time
Use when updating diff The algorithm is updated ,diff The algorithm involves a key, It is used to ensure that the node position can be accurately found and changed , Otherwise, it will cause repeated construction of subsequent nodes , Consume unnecessary performance
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