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]);
    }
  }
}

var re = null, i;
for(i = 0; i < 10; i++){
  re = /cat/g;
  re.test('catastrophe');
}
for(i = 0; i < 10; i++){
  re = new RegExp('cat','g');
  re.test('catastrophe');
}  

var str = 'aaaaabbbbbdddddaaaaaaaffffffffffffffffffgggggcccccce';
var pattern = /(\w)\1+/g;
var maxLength = 0;
var maxValue = '';
var result = str.replace(pattern,function(match,match1,pos,originalText){
  if(match.length > maxLength){
    maxLength = match.length;
    maxValue = match1;
  }
})
console.log(maxLength,maxValue);//18 "f"

//字面量模式  ->       等价的字符串
// /\[bc\]at/ 　　　　　　   "\\[bc\\]at"
// /\.at/ 　　　　　　  　　  "\\.at"
// /name\/age/ 　　  　　  "name\\/age"
// /\d.\d{1,2}/  　　　　  "\\d.\\d{1,2}"
// /\w\\hello\\123/      "\\w\\\\hello\\\\123"

//$$ 　　$
//$& 　　匹配整个模式的子字符串(与RegExp.lastMatch的值相同)
//$`  匹配子字符串之前的子字符串(与RegExp.leftContext的值相同)
//$'  匹配子字符串之后的子字符串(与RegExp.rightContext的值相同)
//$n 　 匹配第n个捕获组子字符串,其中n等于0-9。$1表示匹配第一个捕获组的子字符串(从第1个算起)
//$nn 　 匹配第nn个捕获组的子字符串，其中nn等于01-99

console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$0'))//$0,$0,$0,$0  
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$1'))//ca,ba,sa,fa
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$2'))//t,t,t,t
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$3'))//$3,$3,$3,$3  
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$$'))//$,$,$,$
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$&'))//cat,bat,sat,fat
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,'$`'))//,cat,,cat,bat,,cat,bat,sat,
console.log('cat,bat,sat,fat'.replace(/(.a)(t)/g,"$'"))//,bat,sat,fat,,sat,fat,,fat,

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'

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  
}

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 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'

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'

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 = pattern.exec(string);
while(temp != null){
  valueArray.push(temp[0]);
  indexArray.push(temp.index);
  temp = pattern.exec(string);  
}
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 string = 'cat,bat,sat,fat';
var pattern = /.at/;
var matches = string.match(pattern);
console.log(matches,matches.index,matches.input);//['cat'] 0 'cat,bat,sat,fat' 

var string = 'cat,bat,sat,fat';
var pattern = /.at/g;
var matches = string.match(pattern);
console.log(matches,matches.index,matches.input);//['cat','bat','sat','fat'] undefined undefined

var string = 'cat,bat,sat,fat';
var pattern = 'at';
var matches = string.match(pattern);
console.log(matches,matches.index,matches.input);//['at'] 1 'cat,bat,sat,fat'  

var string = 'cat,bat,sat,fat';
var pattern = /.at/;
var pos = string.search(pattern);
console.log(pos);//0

var string = 'cat,bat,sat,fat';
var pattern = 'at';
var pos = string.search(pattern);
console.log(pos);//1

function fnAllSearch(str,pattern){
  var pos = str.search(pattern); 
  var length = str.match(pattern)[0].length;
  var index = pos+length;
  var result = [];
  var last = index;
  result.push(pos);
  while(true){
    str = str.substr(index);  
    pos = str.search(pattern);
    if(pos === -1){
      break;
  }
  length = str.match(pattern)[0].length;
  index = pos+length;
  result.push(last+pos);
  last += index;  
}
return result;
}  
console.log(fnAllSearch('cat23fbat246565sa3dftf44at',/\d+/));//[3,9,17,22]

var string = 'cat,bat,sat,fat';
var result = string.replace('at','ond');
console.log(result);//'cond,bat,sat,fat'

var string = 'cat,bat,sat,fat';
var result = string.replace(/at/,'ond');
console.log(result);//'cond,bat,sat,fat'

var string = 'cat,bat,sat,fat';
var result = string.replace(/at/g,'ond');
console.log(result);//'cond,bond,sond,fond'

function htmlEscape(text){
  return text.replace(/[<>"&]/g,function(match,pos,originalText){
    switch(match){
      case '<':
        return '<';
      case '>':
        return '>';
      case '&':
        return '&';
      case '\"':
        return '"';
    }
  });
}
console.log(htmlEscape('<p class=\"greeting\">Hello world!</p>'));
//<p class=" greeting">Hello world!</p>
console.log(htmlEscape('<p class="greeting">Hello world!</p>'));
//同上  

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 str1 = 'j1h342jg24g234j 3g24j1';
var array = [];
var temp = '';
for(var i = 0; i < str1.length; i++){
  var value = parseInt(str1.charAt(i));//如果用number将无法排除空格
    if(!isNaN(value)){
      temp += str1.charAt(i);
    }else{
      if(temp != ''){
        array.push(temp);
        temp = '';  
      }
    }
}
if(temp != ''){
  array.push(temp);
  temp = '';  
}
console.log(array);

var str1 = 'j1h342jg24g234j 3g24j1';
array = str1.match(/\d+/g);
console.log(array);

var string = 'FLG是邪教';
var pattern = /FLG|邪教/g;
var result = string.replace(pattern,function($0){
  var s = '';
  for(var i = 0; i < $0.length; i++){
    s+= '*';
  }
  return s;
})
console.log(result);

var array = ['2015.7.28','2015-7-28','2015/7/28','2015.7-28','2015-7.28','2015/7---28'];
function formatDate(date){
  return date.replace(/(\d+)\D+(\d+)\D+(\d+)/,'$1'+'年'+'$2'+'月'+'$3'+'日')
}
var result = [];
for(var i = 0 ; i < array.length; i++){
  result.push(formatDate(array[i]));
}
console.log(result);

var str = '<p>refds</p><p>fasdf</p>'
var pattern = /<[^<>]+>/g;
console.log(str.replace(pattern,''));

var string = ' my name is littlematch ';
console.log(string.replace(/^\s+|\s+$/,''));