1 , 1 The regular expression contains only Chinese characters, Numbers and letters, and the underscore cannot be followed by the beginning and end of the underscore:
^(?!_)(?!.*?_$)[a-zA-Z0-9_\u4e00-\u9fa5]+$  Among them:
^  Matches where the string begins
(?!_) Not to _ At the beginning
(?!.*?_$) Not to _ At the end
[a-zA-Z0-9_\u4e00-\u9fa5]+ At least, 1 Chinese characters, Numbers, letters, underline
$ Matches where the string ends

 Put it in front of the program @ , otherwise \\ escape  @"^(?!_)(?!.*?_$)[a-zA-Z0-9_\u4e00-\u9fa5]+$"
  (or: @"^(?!_)\w*(?<!_)$"   or  @" ^[\u4E00-\u9FA50-9a-zA-Z_]+$ " )

2 , only contains Chinese characters, Numbers, letters, underline, underline position is not limited:
 ^[a-zA-Z0-9_\u4e00-\u9fa5]+$

3 , by Numbers, 26 A string of letters or underscores
^\w+$

4 , 2~4 The Chinese characters
 @"^[\u4E00-\u9FA5]{2,4}$";

5 ,
^[\w-]+(\.[\w-]+)*@[\w-]+(\.[\w-]+)+$

 To use: (Abc)+   To analyze:  XYZAbcAbcAbcXYZAbcAb

XYZAbcAbcAbcXYZAbcAb
6 ,
[^\u4E00-\u9FA50-9a-zA-Z_]
34555#5' -->34555#5'

[\u4E00-\u9FA50-9a-zA-Z_]  eiieng_89_  --->  eiieng_89_
_';'eiieng_88&*9_  --> _';'eiieng_88&*9_
_';'eiieng_88_&*9_ --> _';'eiieng_88_&*9_

public bool RegexName(string str)
 {
  bool flag=Regex.IsMatch(str,@"^[a-zA-Z0-9_\u4e00-\u9fa5]+$");
  return flag;
 }

 Regex  reg=new  Regex("^[a-zA-Z_0-9]+$");
 if(reg.IsMatch(s))
 {
 \\ Comply with the rules
 }
 else
 {
 \\ Invalid character
 }

That’s all for this article, and I hope it will be helpful for you to learn javascript regular expressions.