JS 字符串

             var str = "aaddaabbcdddefg"
             console.log(str.charAt());//b   没有返回空不是null
             console.log(str.indexOf('p'));//1  没有返回-1

             var obj  = {};
             for(var i=;i<str.length;i++){
                 var v = str.charAt(i);
                 if(obj[v] && obj[v].value == v){
                     obj[v].count  ++ ;
                 }else{
                     obj[v] = {};
                     obj[v].count = ;
                     obj[v].value = v;
                 }
             }

             console.log(obj);//true
             //obj =  {a:object,b:object,c:object}
             for(key in obj){
                 document.write(obj[key].value +'='+obj[key].count+'&nbsp;'); // a=4  b=3  c=4  d=2  f=1  g=1  h=1
             }

记录字符串中每一项，并且记录个数