indexOf属性不支持

//此方法是数组的indexof属性不支持特此增加此段代码
if (!Array.prototype.indexOf)
{
Array.prototype.indexOf = function(elt /*, from*/)
{
var len = this.length >>> 0;
var from = Number(arguments[1]) || 0;
from = (from < 0)? Math.ceil(from): Math.floor(from);
if (from < 0) from += len;
for (; from < len; from++)
{
if (from in this && this[from] === elt)
return from;
}
return -1;
};
}