select 或text的onchange事件需要手動（通過鍵盤輸入）改變select或text的值才能觸發，如果在js中給select或text賦值，則無法觸發onchang事件，
例如，在頁面加載完成以後，需要觸發一個onChange事件，在js中用document.getElementById("province").value="湖北";直接給select或text賦值是不行的，要想實現手動觸發onchange事件，需要在js給select賦值後，加入下面的語句
document.getElementById("province").fireEvent('onchange') 來實現,
<head><meta http-equiv="Content-Type" content="text/html; charset=gb2312" /><title>無標題文檔</title><script type="text/javascript">var provinces = new Array();provinces["湖北"] = ["武漢","襄陽","隨州","宜昌","十堰"];provinces["四川"] = ["成都","內江","達州"];provinces["河南"] =["鄭州","南陽","信陽","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 id="province" onchange= "changeProvince()"></select>城市:<select id="city"></select></body></html>