JavaScript常用函数以及语法

 .字符串(String)
1.声明
     var myString = new String("Every good boy does fine.");
     var myString = "Every good boy does fine.";
   2.字符串连接
     var myString = "Every " + "good boy " + "does fine.";
     var myString = "Every ";   myString += "good boy does fine.";
   3.截取字符串
     //截取第 6 位开始的字符
     var myString = "Every good boy does fine.";
     var section = myString.substring(6);     //结果: "good boy does
fine."
   
     //截取第 0 位开始至第 10 位为止的字符
     var myString = "Every good boy does fine.";
     var section = myString.substring(0,10); //结果: "Every good"
   
     //截取从第 11 位到倒数第 6 位为止的字符
     var myString = "Every good boy does fine.";
     var section = myString.slice(11,-6);     //结果: "boy does"
   
     //从第 6 位开始截取长度为 4 的字符
     var myString = "Every good boy does fine.";
     var section = myString.substr(6,4);      //结果: "good"
   4.转换大小写
     var myString = "Hello";
     var lcString = myString.toLowerCase();   //结果: "hello"
     var ucString = myString.toUpperCase();   //结果: "HELLO"
   5.字符串比较
     var aString = "Hello!";
     var bString = new String(&q