Discussion on JavaScript regular expression grouping matching

grammar

Metacharacter: (pattern) function: used for groups that are repeatedly matched

Properties $1 to $9, if they exist, are used to get the substring matched in the corresponding group

\1 or $1 is used to match the contents of the first group

\2 or $2 is used to match the contents of the first group

...

\9 or $9 is used to match the contents of the first group

Usage examples

var reg = /(A+)((B|C|D)+)(E+)/gi;// The regular expression has 4 A grouping 
// Corresponding relations between 
//RegExp.$1 <-> (A+)
//RegExp.$2 <-> ((B|C|D)+)
//RegExp.$3 <-> (B|C|D)
//RegExp.$4 <-> (E+)

The above code also shows the usage of $1~$9

$1~$9 are static properties predefined by the regular expression, referenced by RegExp.$1

Grouping nested relationship description

The code above also illustrates the nesting of groups

// The test environment   Chrome The browser 
var str = "ABCDE";
var reg = /(A+)((B|C|D)+)(E+)/gi;
str.match(reg);// Output: ["ABCDE"]
reg.exec(str,'i');// Output: ["ABCDE", "A", "BCD", "D", "E"]
RegExp.$1;// Output: "A"
RegExp.$2;// Output: "BCD"
RegExp.$3;// Output: "D"
RegExp.$4;// Output: "E"

This makes it easy to see the nesting of groups

To sum up: when there is a small group in a large group, the small group is the group next to the large group, and so on

That's all for this article, I hope you enjoy it.