JavaScript学习（一）——数据类型

var sMyString="hello world";
alert(sMyString.length);    //输出：11

var sMyString="Tsinghua University";
alert(sMyString.charAt(4));                //输出：g

<title>slice()和substring()</title>
<script language="javascript">
var sMyString ="Tsinghua University";
document.write(sMyString.slice(1,3)+"<br>");
document.write(sMyString.substring(1,3)+"<br>");
document.write(sMyString.slice(4)+"<br>");
document.write(sMyString+"<br>");             //不改变原字符串
</script>
//输出： si si ghua University  Tsinghua University

//区别在于对负数的处理方式不同，slice()对负数的处理是从字符串末尾往前计数，而substring()则直接忽略，作为0来处理，例如substring(2,-3)等同于substring(2,0),也等同于substring(0,2)

<title>slice()和substring()的区别</title>
<script language="javascript">
var sMyString=“Tsinghua University”;
document.write(sMyString.slice(2,-3)+"<br>");    　　　　//inghua Univers
document.write(sMyString.substring(2,-3)+"<br>");　　　　//Ts
document.write(sMyString.substring(2,0)+"<br>");　　　　 //Ts
document.write(sMyString+"<br>");                      // Tsinghua University   
</script>

var sMyString ="Tsinghua University";
alert(sMyString.substr(2,3));//输出为第二位开始，取后三位：ing

<title> indexOf()和lastIndexOf()</title>
<script language="javascript">
var sMyString ="Tsinghua University";
document.write(sMyString.indexOf("i")+"<br>");        //从前往后：2
document.write(sMyString.indexOf("i",3)+"<br>");     //可选参数，从第几个字符开始往后找 ：11
document.write(sMyString.lastIndexOf("i")+"<br>");  //从后往前：16
document.write(sMyString.lastIndexOf("i",3)+"<br>");//可选参数，从第几个字符开始往前找：2
document.write(sMyString.lastIndexOf("V")+"<br>"); //大写“V”找不到，返回-1 ：-1
</script>

<script language="javascript">
var fNumber =895.4;
alert(fNumber.toExponential(1));   //输出一位小数：9.0e+2
alert(fNumber.toExponential(2));   //输出两位小数：8.95e+2
<script>

<title>布尔型</title>
<script language="javascript">
var married =true;
alert("1."+typeof(married));           //1.boolean
married="true";
alert("2."+typeof(married));           //2.string
</script>

    <title>类型转换</title>
    <script language="JavaScript">
        var a=3;
        var b=a+"";
        var c=a.toString();
        var d="stidemt"+a;
        alert(typeof(a)+""+typeof(b)+""+typeof(c)+""+typeof(d));//输出均为 string
    </script>  

    <title>toString()方法</title>
    <script language="JavaScript">
        var a=11;
        document.write(a.toString(2)+"<br>");   //转换为2进制：1011
        document.write(a.toString(3)+"<br>");   //转换为3进制：102
        document.write(a.toString(8)+"<br>");   //转换为8进制：13
        document.write(a.toString(16)+"<br>");  //转换为16进制：b
    </script>    

    <title>parseInt()方法</title>
    <script language="JavaScript">
        document.write(parseInt("4567red")+"<br>");   //输出为：4567
        document.write(parseInt("53.5")+"<br>");   //输出为：53
        document.write(parseInt("0xC")+"<br>");   //输出为：12
        document.write(parseInt("isaacshun@gmail.com")+"<br>");  //输出为：NaN
    </script>   

<title>parseInt()方法</title>
    <script language="JavaScript">
        document.write(parseInt("AF",16)+"<br>");   //输出为：175
        document.write(parseInt("11",2)+"<br>");   //输出为：3
        document.write(parseInt("011")+"<br>");   //输出为：9
        document.write(parseInt("011",8)+"<br>");   //输出为：9
        document.write(parseInt("011",10)+"<br>");   //输出为：11
    </script>    

<title>parseFloat()方法</title>
    <script language="JavaScript">
        document.write(parseFloat("34535orange")+"<br>");           //输出为：34535
        document.write(parseFloat("0xA")+"<br>");                   //不会有默认进制，直接输出为第一个字符“0”
        document.write(parseFloat("435.34")+"<br>");                //输出为：435.34
        document.write(parseFloat("435.34.564"+"<br>");             //输出为：435.34
        document.write(parseFloat("isaacshun@gmail.com")+"<br>");   //输出为：NaN
    </script>    
    

    <script language="JavaScript">
        var aMap =new Array("China","USA","Britain");
        aMap[20]="Korea";
        alert(aMap.length);                             //3
        alert(aMap[10]);                                //undefined
        alert(aMap[20]);                                //Korea
    </script>    

    <script language="JavaScript">
        var aMap =new Array("China","USA","Britain");
        alert(aMap.toString()+""+typeof(aMap.toString()));      //China,USA,Britain string                           
    </script> 

<title>join()方法</title>
    <script language="JavaScript">
        var aMap =new Array("China","USA","Britain");
        document.write(aMap.join()+"<br>");             //无参数，等同于toString（）：China,USA,Britain
        document.write(aMap.join("")+"<br>");           //不用连接符    ：ChinaUSABritain
        document.write(aMap.join("][")+"<br>");           //用“][”来连接    ：China][USA][Britain
        document.write(aMap.join("-isaac-")+"<br>");           //用-isaac-连接    ：China-isaac-USA-isaac-Britain
    </script>    

<title>split()方法</title>
    <script language="JavaScript">
       var sFruit ="apple,pear,peach,orange";
       var aFruit=sFruit.split(",");
       alert(aFruit.join("--"));                //输出为：apple--pear--peach--orange
    </script>    

<title>reverse()方法</title>
    <script language="JavaScript">
       var aFruit =["apple","pear","peach","orange"];
       alert(aFruit.reverse().toString());                //输出为：orange,peach,pear,apple
    </script>  

       var sMyString="abcdefg";
       alert(sMyString.split("").reverse().join(""));
       /*split("")将每一个字符转化为一个数组元素
       reverse()反序数组的每个元素
       join("")最后将数组无连接符地转换成为字符串
       */

<title>sort()方法</title>
    <script language="JavaScript">
        var aFruit=["apple","pear","peach","orange"];
        aFruit.sort();
        alert(aFruit.toString());                   //按照大小来排序：apple,orange,peach,pear
    </script> 

<title>栈</title>
    <script language="JavaScript">
       var stack =new Array();
       stack.push("red");
       stack.push("green");
       stack.push("blue");
       document.write(stack.toString()+"<br>");             //输出：red,green,blue
       var vItem=stack.pop();
       document.write(vItem+"<br>");                        //输出：blue
       document.write(stack.toString());                    //输出：red,green
    </script>