Front-end notes-a brief summary of front-end optimization_html/css_WEB-ITnose

Some personal brief summary of front-end optimization, referring to some materials written by others

1. Server aspect:
   
   1. Improve the quality of your own server, bandwidth, etc. Aspects
   2. Enable browser cache to reduce http requests
   3. Enable gzip compression
   4. Use content distribution network cdn
2. html interface
   
   1. Css files are placed in the head, and js files are placed at the end of the html. When downloading a certain JS, other tasks are suspended. You need to wait for this JS to be downloaded and executed before downloading other ones
   2. Inline css is not applicable
   3. Try to reduce tags as much as possible, and do not use more than one tag. For example, clear floating uses: after
   4. js lazy loading, asynchronous loading, use defer tag, async="true"
   5. to reduce dns queries. Every time a file from an external source is referenced, there will be a DNS query, which will generally have an impact on the speed of the first visit to the website
   6. Avoid 404. Encountering 404 when downloading js is a big problem
   7. Avoid empty src, such as src=""
   8. Reduce http requests: image sprite technology, combined with css and js code
3. Code aspect
   
   1. At the end of the project, a compression tool is used to compress css, js
   2. The class of css should not be too long, and there must be a clear hierarchical relationship
   3. Use class when operating styles in js, not in html Inline css and js code
4. JS optimization
   
   1. String concatenation: using = is less efficient, you can use array join() Methods
   2. Especially do not use for (in) when using loops. while is more efficient than for (;;)
   3. Local variables are accessed faster than global variables and should be avoided as much as possible Each operation of global variables
   4. on DOM elements is relatively expensive, so operate it as little as possible. For example, if there is string splicing in the for loop, and then innerHTML is used to operate, the innerHTML should be placed outside the for loop
   5. When operating a certain DOM node, store the DOM node in a local variable
   6. Regarding string traversal, it is preferred to use regular expressions
   7. Variable type conversion
      
   8. Convert numbers into strings ("" )>String()> .toString()>newString()
   9. Convert string to number parseInt()
   10. Conversion between floating point and integer Math.floor() or Math.round()
   11. Using direct variables var a = [] is faster than var a = new Array()
   12. It is best not to write strings directly when creating DOM nodes, but to call the creatElement() method