如果有一个Javascript错误，你应该看到它在浏览器控制台，并与我们分享。
在任何情况下，我都会先创建一个JS对象，我发现这样更容易操作。
在下面的代码中，我添加了检查querystring的多个参数的选项。如果你只需要检查IC，你可以稍微简化它。我在一个空白的test.html上测试了它。

<script type="text/javascript">
// get the current params of the querystring
var querystringItems = document.location.search.substr(1).split('&');

// create an object
var querystringObject = {};
for(i=0;i<querystringItems.length;++i) {
    param = querystringItems[i].split('=');
    querystringObject[param[0]] = param[1];
}

// Define the keys to be searched for and their default value when they are not present
var requiredKeys = {"IC":48, "test": "me"};

// Do the checking on the querystringObject for each requiredKeys
var doreload = false;
for (var key in requiredKeys) {
    if (typeof querystringObject[key] == 'undefined') {
        doreload = true;
        // Create the missing parameter and assign the default value
        querystringObject[key] = requiredKeys[key];
    }
}

// If any of the requiredKeys was missing ...
if (doreload) {
    // rebuild the querystring
    var querystring = '?';
    for (var key in querystringObject) {
        querystring+=key+'='+querystringObject[key]+'&';
    }
    querystring=querystring.substr(0,querystring.length-1);
    // reload page
    document.location.search = querystring;
}

// assign the values to javascript variables (assuming you had it like this because you needed it)
var itemsPerPage = querystringObject.IC;
</script>

下面是一个示例来检查这一点：

//get URL params into string:
paramStr = window.location.substring(window.location.indexOf('?'), window.location.length;
//turn string into array
paramArray = paramStr.split('&');
//prepare final array of params
params = {};
//prepare the index of IC parameter
icLoc = -1; //this is negative 1 so that you know if it was found or not
//for each item in array
for(var i in paramArray){
    //push its name and value to the final array
    params.push(paramArray[i].split('='));
    //if the parameter name is IC, output its location in array
    if(params[i][0] === 'IC'){
        icLoc = i;
    }
}

如果未找到IC，则icLoc将为-1。
如果找到，则URL参数中IC的值为params[icLoc][1]
查询字符串?foo=bar&code=cool&IC=HelloWorld的结果示例：

params = {'foo': 'bar', 'code': 'cool', 'IC': 'HelloWorld'}
icLoc = 2

查询字符串?foo=bar&code=cool的示例：

params = {'foo': 'bar', 'code': 'cool'}
icLoc = -1

这里的id是我在测试中使用的参数，传递你想要检查它是否存在的参数。

function queryParamExistUrl(param = '') {
            if (new URLSearchParams(window.location.search).get(param) != null)
                return true
            return false
        }
        console.log(queryParamExistUrl('id'))