JavaScript正则表达式的分组匹配详解

/kidkidkid/

/(kid){3}/

var reg = /I love (him|her|it)/;

reg.test('I love him')  // true 
reg.test('I love her')  // true
reg.test('I love it')  // true
reg.test('I love them') // false

var reg = /(\d{4})-(\d{2})-(\d{2})/
var date = '2010-04-12'
reg.test(date)

RegExp.$1 // 2010
RegExp.$2 // 04
RegExp.$3 // 12

var reg = /(\d{2}).(\d{2})\/(\d{4})/
var date = '12.21/2012'

date = date.replace(reg, '$3-$1-$2') // date = 2012-12-21

var reg = /(kid|doubi)/g
var str = 'kid is a doubi'

str = str.replace(reg, function(word){
  return word.replace(/./g, '*')
})

var reg = /((kid) is (a (doubi)))/
var str = "kid is a doubi"

reg.test( str ) // true

RegExp.$1 // kid is a doubi
RegExp.$2 // kid
RegExp.$3 // a doubi
RegExp.$4 // doubi

var reg = /(\w{3}) is \1/

reg.test('kid is kid') // true
reg.test('dik is dik') // true
reg.test('kid is dik') // false
reg.test('dik is kid') // false

var reg = /(\w{3}) is \6/;

reg.test( 'kid is kid' ); // false
reg.test( 'kid is \6' );  // true

var reg = /(?:\d{4})-(\d{2})-(\d{2})/
var date = '2012-12-21'
reg.test(date)

RegExp.$1 // 12
RegExp.$2 // 21

var reg = /kid is a (?=doubi)/

reg.test('kid is a doubi') // true
reg.test('kid is a shabi') // false

var reg = /kid is a (?!doubi)/

reg.test('kid is a doubi') // false
reg.test('kid is a shabi') // true

var reg, str = "kid is a doubi"

reg = /(kid is a (?:doubi))/
reg.test(str)
RegExp.$1 // kid is a doubi

reg = /(kid is a (?=doubi))/
reg.test(str)
RegExp.$1 // kis is a