//匹配字符串所有'at'的实例
var p = /at/g;
//test()方法返回一个布尔值表示是否可以找到匹配项
console.log(p.test('ata'));//true
console.log(p.test('aba'));//false

//匹配字符串所有'at'的实例
var p1 = /at/g;
//同上
var p2 = new RegExp('at','g');

function getByClass(obj,classname){
  var elements = obj.getElementsByTagName('*');
  var result = [];
  var pattern = new RegExp( '(^|\\s)'+ classname + '(\\s|$)');
  for(var i = 0; i < elements.length; i++){
    if(pattern.test(elements[i].className)){
      result.push(elements[i]);
    }
  }
  return result;
}

global:　　  布尔值，表示是否设置了g标志
ignoreCase: 布尔值，表示是否设置了i标志
lastIndex:  整数，表示开始搜索下一个匹配项的字符位置，从0算起
multiline:  布尔值，表示是否设置了标志m
source: 　　 正则表达式的字符串表示，按照字面量形式而非传入构造函数中的字符串模式返回

var pattern = new RegExp('\\[bc\\]at','i');
console.log(pattern.global);//false
console.log(pattern.ignoreCase);//true  
console.log(pattern.multiline);//false
console.log(pattern.lastIndex);//0
console.log(pattern.source);//'\[bc\]at'

//exec()方法以数组形式返回匹配项
var p = /\w/g;
var s = 'ab';
console.log(p.lastIndex);//0
console.log(p.exec(s));//['a']
console.log(p.lastIndex);//1
console.log(p.exec(s));//['b']
console.log(p.lastIndex);//2
console.log(p.exec(s));//null
console.log(p.lastIndex);//0

var p = /\w/g;
var s1 = 'ab';
var s2 = 'ba';
console.log(p.lastIndex);//0
console.log(p.exec(s1));//['a']
console.log(p.lastIndex);//1
console.log(p.exec(s2));//['a']
console.log(p.lastIndex);//2

长属性名    短属性名    　　　　   说明
input       $_        最近一次要匹配的字符串
lastMatch     $&        最近一次的匹配项
lastParen     $+        最近一次匹配的捕获组
leftContext    $`        input字符串中lastMatch之前的文本
multiline     $*        布尔值，表示是否所有表达式都使用多行模式
rightContext   $'        Input字符串中lastMarch之后的文本

//test()用于测试一个字符串是否匹配某个正则表达式，并返回一个布尔值
var text = 'this has been a short summer';
var pattern = /(.)hort/g;
if(pattern.test(text)){
  console.log(RegExp.input);//'this has been a short summer'
  console.log(RegExp.leftContext);//'this has been a '
  console.log(RegExp.rightContext);//' summer'
  console.log(RegExp.lastMatch);//'short'
  console.log(RegExp.lastParen);//'s'
  console.log(RegExp.multiline);//false
  console.log(RegExp['$_']);//'this has been a short summer'
  console.log(RegExp['$`']);//'this has been a '
  console.log(RegExp["$'"]);//' summer'
  console.log(RegExp['$&']);//'short'
  console.log(RegExp['$+']);//'s'
  console.log(RegExp['$*']);//false    
}

//RegExp.$1\RegExp.$2\RegExp.$3……到RegExp.$9分别用于存储第一、第二……第九个匹配的捕获组
var text = 'this has been a short summer';
var pattern = /(..)or(.)/g;
if(pattern.test(text)){
  console.log(RegExp.$1);//sh
  console.log(RegExp.$2);//t
}

var pattern = new RegExp('[bc]at','gi');
console.log(pattern.toString()); // '/[bc]at/gi'
console.log(pattern.toLocaleString()); // '/[bc]at/gi'
console.log(pattern.valueOf()); // /[bc]at/gi

var pattern = /[bc]at/gi;
console.log(pattern.toString()); // '/[bc]at/gi'
console.log(pattern.toLocaleString()); // '[bc]at/gi'
console.log(pattern.valueOf()); // /[bc]at/gi

var text = 'mom and dad and baby and others';
var pattern = /mom( and dad( and baby)?)?/gi;
var matches = pattern.exec(text);
console.log(pattern,matches);
//pattern.lastIndex:20
//matches[0]:'mom and dad and baby'
//matches[1]:' and dad and baby'
//matches[2]:' and baby'
//matches.index:0
//matches.input:'mom and dad and baby and others'

var text = 'cat,bat,sat,fat';
var pattern1 = /.at/;
var matches = pattern1.exec(text);
console.log(pattern1,matches);
//pattern1.lastIndex:0
//matches[0]:'cat'
//matches.index:0
//matches.input:'cat,bat,sat,fat'

var text = 'cat,bat,sat,fat';
matches = pattern1.exec(text);  
console.log(pattern1,matches);  
//pattern1.lastIndex:0
//matches[0]:'cat'
//matches.index:0
//matches.input:'cat,bat,sat,fat'

var text = 'cat,bat,sat,fat';
var pattern2 = /.at/g;
var matches = pattern2.exec(text);
console.log(pattern2,matches);  
//pattern2.lastIndex:3
//matches[0]:'cat'
//matches.index:0
//matches.input:'cat,bat,sat,fat'

var text = 'cat,bat,sat,fat';
matches = pattern2.exec(text);
console.log(pattern2,matches);  
//pattern2.lastIndex:7
//matches[0]:'bat'
//matches.index:4
//matches.input:'cat,bat,sat,fat'

var string = 'j1h342jg24g234j 3g24j1';
var pattern = /\d/g;
var valueArray = [];//值
var indexArray = [];//位置
var temp;
while((temp=pattern.exec(string)) != null){
  valueArray.push(temp[0]);
  indexArray.push(temp.index); 
}
//["1", "3", "4", "2", "2", "4", "2", "3", "4", "3", "2", "4", "1"] [1, 3, 4, 5, 8, 9, 11, 12, 13, 16, 18, 19, 21]
console.log(valueArray,indexArray);

var text = '000-00-000';
var pattern = /\d{3}-\d{2}-\d{4}/;
if(pattern.test(text)){
  console.log('The pattern was matched');
}

var pattern = /^\d{4}-\d{2}-\d{2}$/g;
console.log(pattern.test('2016-06-23'));//true
console.log(pattern.test('2016-06-23'));//false

//正确的做法应该是在验证不同字符串前，先将lastIndex重置为0
var pattern = /^\d{4}-\d{2}-\d{2}$/g;
console.log(pattern.test('2016-06-23'));//true
pattern.lastIndex = 0;
console.log(pattern.test('2016-06-23'));//true

if(/^(\d{4})-(\d{2})-(\d{2})$/.test('2016-06-23')){
  console.log(RegExp.$1);//'2016'
  console.log(RegExp.$2);//'06'
  console.log(RegExp.$3);//'23'
  console.log(RegExp.$0);//undefined
}