//indexOf,chatAt,charCodeAt,substr,substring,concat
//search,replace,match,slice,split
//toLocaleLowerCase,toLocaleUpper,toLowerCase,toUpperCase
var str="Hello World";
console.log(str.indexOf('ll',2));//从第三个字符开始查找ll字符串,返回其索引或-1
console.log(str.charAt(7));//返回第八个字符:o
console.log(str.charCodeAt(7));//返回o的unicode值:111
console.log(str.substr(6,5));//返回起始下标为6长度为5的字符串:World
console.log(str.substring(6,11));//返回下标为6到下标为11的字符串:World
console.log(str.concat(" of JS"));//字符串拼接:Hello World of JS
console.log(str.search('ll',2));//从第三个字符开始查找ll字符串,返回其索引或-1
console.log(str.replace('o','O'));//将str中第一个o替换成O:HellO World
console.log(str.match(/[a-n]/g));//返回一个由str中a-n之间的字符组成的数组: ["e", "l", "l", "l", "d"]
console.log(str.slice(6,11));//提取并返回下标为6到下标为11的字符串片段:World
console.log(str.split(""));//把字符串分割成字符串数组:["H","e","l","l","o","","W","o","r","l","d"]
console.log(str.toLocaleUpperCase());//字符串转换成大写:HELLO WORLD
console.log(str.toLocaleLowerCase());//字符串转换成小写:hello world
console.log(str.toUpperCase());//字符串转换成大写:HELLO WORLD
console.log(str.toLowerCase());//字符串转换成小写:hello world
console.log(str);//以上字符串方法均不改变原字符串