Grouping concept and usage examples of javascript regular expressions

The grouping concept and usage of javascript regular expressions are illustrated with examples.Share it for your reference, as follows:

function matchDemo(){
  var s;
  // The expression is divided 3 Groups: d(b+)(d) , (b+) , (d) this 3 Group (actually 4 Groups, including all expressions of their own) 
  // From the leftmost number 1 Brackets are # 1 Groups, No. 2 Brackets are # 2 Group, and so on, where the values are RegExp.$1 and RegExp.$2 Value of 
  var re = new RegExp("(d(b+)(d))","ig");
  var str = "cdbBdbsbdbdz";
  //exec() The returned value was found by matching the expression 1 Arrays 
  var arr = re.exec(str);
  // accord with d(b+)(d) The value returned by this expression 
  s = "$1 contains: " + RegExp.$1 + ", RegExp.$1 : " + RegExp.$1.length + "\n";
  // accord with (b+) The value returned by this expression 
  s += "$2 contains: " + RegExp.$2 + ", RegExp.$2 : " + RegExp.$2 + "\n";
  // accord with (d) The value returned by this expression 
  s += "$3 contains: " + RegExp.$3 + ", RegExp.$3 : " + RegExp.$3;
  // Get the last matching string 1 The position of characters in the string, that is, the start of the next match 
  alert(RegExp.lastIndex);
  // If a value exists, the last one is returned 1 Grouped results ( Returns the last parenthesis sub-match of any regular expression lookup )
  alert(RegExp.lastParen);
  // Get the last matching string ( Returns the last matching character in any regular expression search )
  alert(RegExp.lastMatch);
  //leftContext + lastMatch + rightContext == context
  alert(RegExp.leftContext);
  alert(RegExp.rightContext);
  // The result is 2 Grouped results 
  alert(RegExp.$2);
  return(s);
}
alert(matchDemo());

function matchDemo2(){
  var s,temp;
  // The results are divided into two groups (b+) , (d) And, of course, all of them (d(b+)(d)) Is the default group 
  var re = new RegExp("d(b+)(d)","ig");
  var str = "cdbBdbsbdbdz";
  //arr Results include 3 Groups ( Include all modes ) Return Results 
  //dbBd , bB , d and dbd , b , d The two patterns match, while the 2 And 3 The number of arrays is actually in the 1 Match on the basis of (b+) , (d) Both modes 
  // That is, the grouping is matched in the fully matched mode, so as to " screen " Functions 
  while((arr = re.exec(str)) != null)
  {
      alert(arr);
      temp = "$1 contains: " + RegExp.$1 + ", RegExp.$1.length : " + RegExp.$1.length + ",RegExp.$1.lastIndex:" + RegExp.$1.lastIndex; 
      alert(temp);
      //$2 The attribute represents the matching number 2 Groups, that is (d) This mode 
      s = "$2 contains: " + RegExp.$2 + ", RegExp.$2.length : " + RegExp.$2.length;
      alert(s);
  }
}
matchDemo2();

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I hope that the description in this paper will be helpful to everyone's JavaScript program design.