The onchange event of select or text needs to be manually (via keyboard input) changing the value of select or text in order to be triggered. If you assign a value to select or text in js, the onchang event cannot be triggered,
For example, after the page is loaded, an onChange event needs to be triggered. In js, it is not possible to use document.getElementById("province").value="Hubei"; to directly assign a value to select or text. If you want to manually trigger the onchange event , you need to add the following statement
document.getElementById("province").fireEvent('onchange') to achieve,
<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 id="province" onchange= "changeProvince()"></select>
城市:<select id="city"></select>
</body>
</html>
SQL statement to backup database
Several ways to capture data
How to solve errorreport
Complete collection of SQL query statements
What is the difference between a router and a cat?
ubound function usage
How to set font in css
What is the reason why the computer screen is black but the computer is on?
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
