## 字符串常用的方法
### 1.1 length //獲取字符串的長度
~~~
var a = "hello world";
alert(a.length) //11
~~~
### 增加1.2 concat() 方法用于連接兩個或多個字符串。
~~~
var a = "hello world";
var b = "good";
var c = a.concat(b);
console.log(c);
~~~
### 查詢1.3 charAt(index) //獲取在指定下標的字符
~~~
var a = "hello world";
alert(a.charAt(0)) //
~~~
### 1.4 indexOf(value) 檢索字符串出現的位置
~~~
var a = "hello world";
var b = a.indexOf(“h”); //0;
var c = a.indexOf(“a”); //-1如果沒有返回-1
~~~
### 1.5 stringObject.slice(start,end)
~~~
var a = "hello world";
var b = a.slice(0,2);
console.log(b); //”he”
~~~
### 1.6 stringObject.substr(start,length)
~~~
var a = "hello world";
var b = a.substr(0,5);
console.log(b); //hello
~~~
### 1.7 stringObject.substring(start,stop)
~~~
var a = "hello world";
var b = a.substring(0,2);
console.log(b); //”he”
~~~
### 1.8 split() 方法用于把一個字符串分割成字符串數組。
~~~
stringObject.split(separator,howmany)
var a = "hello world";
var b = a.split("");
console.log(b);
~~~
### 1.9 str.search() //返回下標
~~~
var a = "hello world";
console.log(a.search("h"));
~~~
### 1.10 match()返回數組
~~~
var a ="hello";
console.log(a.match("l"));
~~~
### 1.11 replace()替換
~~~
var a ="hello";
var b = a.replace("l","*");
console.log(b);
~~~
