尝试回叫功能时我做错了

Question

I am trying to use a call back function for this function in javascript

function Filtering_GetSite(siteElement) {

$.ajax({

    type: "POST",
    url: "samle.asmx/f1",
    data: "",
    contentType: "application/json; charset=utf-8",
    dataType: "json",

    success: function (response) {

        var filtersitedetails = response.d;
        var appendItem = "";

        $(siteElement).empty();

        $.each(filtersitedetails, function (index, Filtering_GetSiteInfo) {

            var activeappend = "";
            var id = Filtering_GetSiteInfo.id;
            var site = Filtering_GetSiteInfo.site;

            activeappend = "<option value=" + id + ">" + site + "</option>";

            appendItem += activeappend;

        });

        $(siteElement).prepend('<option disabled="disabled" selected="selected" value="">Select Site</option>');
        $(siteElement).append(appendItem);

    },

    error: function (response) {
        alert("error in Filtering_GetSite");
    }
});
}

and this is how I call the function and trying to use call back function

Filtering_GetSite("#txt-site-name", function () {
           alert('ok')
           Dashboard_GetAgentInfo(agentParam,agentElement);
       });

but the problem is it doesn't go to the alert when the function is finished. How can I do this?

Answer 1

That is because you do not seem to pass and invoke that method when the ajax invokes successfully.

First you will have to change the method signature of Filtering_GetSite to accept a 2nd parameter which in this case is the callback and then when the ajax is a success you just invoke it.

function Filtering_GetSite(siteElement, callback) {
   ...

   success: function() {
      ....

      callback();
   }

   ...
}

Answer 2

You haven't set your callback parameter into your Filtering_GetSite function. eg

function Filtering_GetSite(siteElement, callback) {
}

You can then call the callback with callback() where you want it to fire. For example within the success block;

Answer 3

This is a wrap.

You need to specificy a second parameter for a callback function

I also added a condition so when you omit the second parameter it will check the callback if its a function or not so you can call the function just Filtering_GetSite(sample) insted of Filtering_GetSite(sample,function(){})

function Filtering_GetSite(siteElement, callback) {
 if (typeof (callBack) == "function") {
            callBack();
        }
}