4.07字符串与数组的一些常用方法

1. concat()拼装
   let str = "html".concat("css","js","php","!",888);
htmlcssjsphp!888
2. slice(start,end)取子串

   str = "hello php.cn";
   let res = str.slice(0,5);
   console.log(res);//hello
   res = str.slice(6);
   console.log(res);//php.cn

   3.substr(start,size)取子串

   res = str.substr(0,5);
   console.log(res);//hello

   4.trim():删除字符串两边的空白字符

   let pw = "    888    ";
   console.log(pw.length);//11
   console.log(pw.trim());//888

   5.split() 将字符串打散成数组

   res = str.split("");
   console.log(res);//["h", "e", "l", "l", "o", " ", "p", "h", "p", ".", "c", "n"]
   let email = "demo@mail.com";
   res = email.split("@");
   console.log(res);//["demo", "mail.com"]
   console.log('userName = ',res[0]);//userName =  demo
   console.log('emailAddress = ',res[1]);//emailAddress =  mail.com

   6.replace() 替换字符串内容

   res = email.replace("demo","admin")
   console.log(res);// admin@mail.com

   数组方法

   1.pop() 从数组中删除最后一个元素

   arr = ["Banana", "Orange", "Apple", "Mango"];
   arr.pop();
   console.log(arr);// ["Banana", "Orange", "Apple"]

   2.push() 在结尾处向数组添加一个新的元素

   arr.push("Cherry");
   console.log(arr);// ["Banana", "Orange", "Apple", "Cherry"]

   3.shift() 删除首个数组元素

   arr.shift();
   console.log(arr);// ["Orange", "Apple", "Cherry"]

   4.unshift() 将新元素添加到数组的开头

   arr.unshift("Lemon");
   console.log(arr);// ["Lemon", "Orange", "Apple", "Cherry"]