javascript 数组的定义和数组的长度

var a = new array();
var b = new array(8);
var c = new array("first", "second", "third");

var myarray = [];
myarray[myarray.length] = 'new element';

<script>
var a = new Array("first", "second", "third")
a[48] = "12"
document.write(a.length)
//显示的结果是49
</script>

var myarray = [1,2,3];
myarray.length // 初始的长度是3
myarray.length = 2; // 删除最后一个元素
myarray.length = 20 // 添加18个元素到数组中