make ajax call from javascript code example

Example 1: ajax call

$.ajax({
        url: "Url",
        dataType: "json",
        type: "Post",
        async: true,
        data: {"Key":value,"Key2":value2},
        success: function (data) {
                
        },
        error: function (xhr, exception, thrownError) {
            var msg = "";
            if (xhr.status === 0) {
                msg = "Not connect.\n Verify Network.";
            } else if (xhr.status == 404) {
                msg = "Requested page not found. [404]";
            } else if (xhr.status == 500) {
                msg = "Internal Server Error [500].";
            } else if (exception === "parsererror") {
                msg = "Requested JSON parse failed.";
            } else if (exception === "timeout") {
                msg = "Time out error.";
            } else if (exception === "abort") {
                msg = "Ajax request aborted.";
            } else {
                msg = "Error:" + xhr.status + " " + xhr.responseText;
            }
            if (callbackError) {
                callbackError(msg);
            }
           
        }
    });

Example 2: ajax syntax in javascript

var id = empid;

$.ajax({
    type: "POST",
    url: "../Webservices/EmployeeService.asmx/GetEmployeeOrders",
    data: "{empid: " + empid + "}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function(result){
        alert(result.d);
        console.log(result);
    }
});

Example 3: js functional ajax requests

function checkUserIdExists(userid, callback) {
        return $.ajax({
        url: 'theurl',
        type: 'GET',
        cache: false,
        data: {
           userid: userid
        }
    })
    .done(callback)
    .fail(function(jqXHR, textStatus, errorThrown) {
        // Handle error
    });
}

checkUserIdExists(2, function(data) {
    console.log(data); // Do what you want with the data returned
});