1.数组的引出

用数组解决王大爷养乌龟的问题：

var weights=[3,5,1,3.4,2,50];

var all_weight=0;

var avg_weight=0;

for (i=0;i<weights.length ;i++){

	  all_weight+=weights[i];

  }

  //假设想知道数据类型

  //window.alert(avg_weight.constructor);

avg_weight=all_weight/weights.length;

document.writeln('乌龟的整体重是'+all_weight+" "+'平均体重是'+avg_weight.toFixed(2));

2.数组的细节

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数组在内存中的存在形式：

1）传递详细的值，不会更改

var myval=900;

function abc(val){

   val=90;

 }

abc(myval);

window.alert(myval);

执行图：

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2）传递引用地址

var myarr=[456,50,90]

function abc2(arr){

   arr[0]=35;

}

abc2(myarr);

window.alert(myarr);

执行图：

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3）数组的引用

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案例：

var a=[23,'hello',4.4,'ture'];

window.alert(a[3]);

window.alert(a[4]);

结论：不能訪问不存在的元素。数组下标是从0開始编号的。

4）js的数组能够动态增长

var a=[2,3];

alert('size='+a.length);

a[2]=56;//动态的增长

alert('size='+a.length);

window.alert(a[2]);

5）对字符串切割，生成一个字符串数组

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①

var str="hello world abc 顺平";

var arr=str.split(" ");

for (i=0;i<arr.length ;i++ )

{

	document.write(arr[i]+" ")

}

document.write('</br>')

②

var str="hello world abc 顺平";

document.write(str.split(" "));