js常用字符串操作

var str = "abcdefg";
console.log(str.substring(2,5));   //返回 cde
console.log(str.substring(4));     //返回 efg

String.prototype.stitas = function(){
var json = {};
for (var i = 0; i < this.length; i++) {
if(!json[this[i]]){
json[this[i]] = 1;
}else{
json[this[i]]++;
}
}
var max = 0;
var str = "";
for(var i  in json){
if(json[i] > max){
max = json[i];
str = i;
}
}
return max+","+str;
}

str = 'dfbfdgngmhj,hj.,';
console.log(str.stitas());

var str = "aa bb cc aa";
var rName = "aa";
//已知变量时将aa->qq
str = str.replace(/aa/, "qq");
//未知变量时aa->qq
str = str.replace(new RegExp( "(\\s|^)" + rName + "(\\s|$)" ),"qq");
console.log(str);

var a = 00897;
console.log((Number(a)+"").length);