DOM笔记（九）：引用类型、基本包装类型和单体内置对象

//Array构造函数(可以去掉new)
var colors0 = new Array();
var colors1 = new Array(20);
var colors3 = new Array("red","blue","green");

//数组字面量
var colors4 = ["red","blue","green"];
var colors5 = [];

//检测某个对象是不是数组
if(value instanceof Array)
{
  //操作
}
//instanceof只在只有一个全局执行环境时才有效，对于多框架网页，此方法不适合
//ECMAScript5 新增isArray()方法，可以解决instanceof的问题

if(Array.isArray(value))
{
  //操作
}

var colors = ["red","blue","green"];
//均显示red,blue,green
alert(colors.toString());
alert(colors.valueOf());
alert(colors);

var person1 = 
{
    toLocaleString:function()
    {
        return "test1";
    },
    toString:function()
    {
        return "test2";
    }
};
var person2 = 
{
    toLocaleString:function()
    {
        return "dwqs";
    },
    toString:function()
    {
        return "ido321";
    }
};
var people = [person1,person2];
alert(people);                     //test2,ido321
alert(people.toString());          //test2,ido321
alert(people.toLocaleString());    //test1,dwqs

var colors = new Array();
var count = colors.push(‘red‘,‘green‘);   //推入两项，并返回修改后的数组长度
alert(count);  //2
count = colors.push("black");
alert(count);  //3
var item = colors.pop();
alert(item);  //black
alert(colors.length); //2

var colors = new Array();
var count = colors.push(‘red‘,‘green‘);   //推入两项，并返回修改后的数组长度
alert(count);  //2
count = colors.push("black");
alert(count);  //3
var item = colors.shift();
alert(item);  //black
alert(colors.length); //2

//reverse反序
var values1 = [1,2,3,4,5];
alert(values1.reverse());  //5,4,3,2,1
//sort排序
var values2 = [0,1,5,10,15];
alert(values2.sort());  //0,1,10,15,5

function compare(value1, value2)
{
    if(value1 < value2)
    {
        return -1;
    }
    else if(value1 > value2)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}
var values2 = [0,1,5,10,15];
alert(values2.sort(compare));  //0,1,5,10,15

//every函数
var numbers = [1,2,3,4,5,4,3,2,1];
var everyResult = numbers.every(function(item,index,array)
{
   return (item > 2);
});
alert(everyResult);  //false
//some函数
var someResult = numbers.some(function(item,index,array)
{
   return (item > 2);
});
alert(someResult);  //true

var colors = ["red","green","blue"];
//concat()：基于当前数组返回一个新的数组
var colors2 = colors.concat("yellow",["black","brown"]);
alert(colors);     //red,green,blue
alert(colors2);    //red,green,blue,yellow,black,brown

//slice():基于当前数组的一个或多个项创建一个新数组
var colors3 = colors2.slice(1);
var colors4 = colors2.slice(1,4);
alert(colors3);    //green,blue,yellow,black,brown
alert(colors4);    //green,blue,yellow(不包括位置4的元素)

//splice():对数组元素进行删除、插入和替换
//1、删除：指定两个参数，要删除的第一项的位置和删除的项数,返回从数组中删除的项
var removed = colors3.splice(1,2);
alert(colors3);  //green,black,brown
alert(removed);  //blue,yellow

//2、插入和替换：三个参数，起始位置、要删除的项数和插入的项
//若第二个参数是0，执行插入，返回空数组；不为0，则执行替换，返回删除的项组成的数组
var newcolors = ["red","green","blue"];
var removed2 = newcolors.splice(1,2,"yellow","orange");
alert(newcolors);    //red,yellow,orange
alert(removed2);  //green,blue

var values = [1,2,3,4,5];
var sum = values.reduce(function(prev,cur,index,array){
    return prev+cur;
});
alert(sum);  //15

//基于当前时间
var now0 = new Date();  
//基于指定的日期字符串
var now1 = new Date(Date.parse("May 25,2004")); 
//基于UTC时间创建
var now2 = new Date(Date.UTC(2014,11,16));

function sum(num1,num2)
{
     return num1+num2;
}
function applySum(num1,num2)
{
     return sum.apply(this,arguments); //return sum.apply(this,[num1,num2]); 
}
function callSum(num1,num2)
{
     return sum.call(this,num1,num2);
}
alert(applySum(10,10));  //20
alert(callSum(10,20));  //30

var s1 = "test string";
var s2 = s1.substring(4);
alert(s2);  //string

//后台等价的代码
var s1 = new String("test string");
var s2 = s1.substring(4);
s1 = null;

var s1="test string";
s1.color = "red";   
alert(s1.color);  //undefined

var value = "25";
var number = Number(value);
alert(typeof number);  //number

var obj = new Number(value);
alert(typeof obj);  //object

//注意点
var falseObject = new Boolean(false);
var result0 = falseObject && true;
alert(result0);  //true;

var falseValue = false;
var result1 = falseValue && true;
alert(result1);  //false;

//区别
alert(typeof falseObject);  //object
alert(typeof falseValue); //boolean
alert(falseObject instanceof Boolean);  //true;
alert(falseValue instanceof Boolean); //false

var num = 10;
alert(num.toString()); //"10"
alert(num.toString(2)); //"1010"
alert(num.toString(8)); //"12"
alert(num.toString(10)); //"10"
alert(num.toString(16)); //"a"

//toFixed(number):返回指定小数位数的数值字符串形式,
var num = 10;
var num1 = 10.005;
alert(num.toFixed(2));  //"10.00"
alert(num1.toFixed(2));  //"10.01"
//toExponential(number):返回指数表示的字符串形式
alert(num.toExponential(1));  //"1.0e+1"
//toPrecision(number):返回上述两种方式中最合适的一种
var num2 = 99;
alert(num2.toPrecision(1));  //"1e+2"
alert(num2.toPrecision(2));  //"99"
alert(num2.toPrecision(3));  //"99.0"

var x3 = "test";
var x=3;
var y = eval("x"+x);
alert(y);  //test