select 或text的onchange事件需要手动（通过键盘输入）改变select或text的值才能触发，如果在js中给select或text赋值，则无法触发onchang事件，
例如，在页面加载完成以后，需要触发一个onChange事件，在js中用document.getElementById("province").value="湖北";直接给select或text赋值是不行的，要想实现手动触发onchange事件，需要在js给select赋值后，加入下面的语句
document.getElementById("province").fireEvent('onchange') 来实现,
<head> <meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> <title>无标题文档</title> <script type="text/javascript"> var provinces = new Array(); provinces["湖北"] = ["武汉","襄阳","随州","宜昌","十堰"]; provinces["四川"] = ["成都","内江","达州"]; provinces["河南"] =["郑州","南阳","信阳","漯河"]; function changeProvince() { var prov = document.getElementById("province").value; var city =document.getElementById("city"); city.options.length =0; for(var i in provinces[prov]) { city.options.add(new Option(provinces[prov][i],provinces[prov][i])); } } window.onload = function(){ var province = document.getElementById("province"); for(var index in provinces) { //alert(index); province.options.add(new Option(index,index)); } province.fireEvent("onchange"); }; </script> </head> <body> 省份:<select onchange= "changeProvince()"></select> 城市:<select></select> </body> </html>
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