jQuery AJAX函数被多次调用但数据仅在第一次调用时被提取

Question

I have a jQuery function for pulling data from an XML file on a flask server. I start out my ready function with calling this function and all of my variables update with no issues. However, when I call the function a second time from a click action my variables do not update. I know that the AJAX function is being called successfully because I get my alerts. It seems as thought the XML document is not being re-loaded after the first call. How can I get my variables to update on every call to the function.

Global Variables

//Variables representing Sensor Data
var bspeed=0;
var set_temp=0;
var f_temp=0;
var fuel_level=0;
var s_temp=0;
var humidity=0;
var bspeed_data=0;
var set_temp=0;
var mode = "mod";
var mod_mode = "blower";

Data-Pull function

//AJAX XML file parsing
function pull_data(){

//Gather Data from main.xml and store into variables
$.ajax({
    type: "GET",
    url: "static/main.xml",
    async: false,
    success: function(xml){
        $(xml).find('item').each(function(){
            var id = $(this).find('id').text();
            switch(id){
                case "ftemp_data":
                    f_temp = $(this).find('value').text();
                    break;
                case "stemp_data":
                    s_temp = $(this).find('value').text();
                    break;
                case "fuel_level_data":
                    fuel_level = $(this).find('value').text();
                    break;
                case "humidity_data":
                    humidity = $(this).find('value').text();
                    break;
                case "blower_speed":
                    alert("Changing bspeed");
                    bspeed_data = $(this).find('value').text();
            }
        });
        alert("Pull Success "+ bspeed_data);
    },
    error: function(data){
        alert("AJAX failed: "+ data.status + ' ' + data.statusText);
    }
});

//Populate HTML with variables
$("#ftemp_data").text(f_temp+("\u00B0"));
$("#stemp_data").text(s_temp+("\u00B0"));
$("#fuel_level_data").text(fuel_level+"%");
$("#humidity_data").text(humidity+"%");
$("#bspeed_data").text(bspeed_data);
}

Ready Function (Simplified)

$(document).ready(function(){
    pull_data();
    //Click Refresh Button
    $("#refresh_btn").click(function(){
        pull_data();
    }); 
}

I'm fairly new to web development so feel free to point out structural issues with what I'm doing.

Answer 1

Probably you need to force to refresh the cache, in order to do this, add a property cache: false in the ajax code:

$.ajax({
    type: "GET",
    url: "static/main.xml",
    async: false,
    cache: false,...

You can check in Jquery Ajax documentation

Answer 2

I think you are getting the cached response, you need to add timestamp to the url ,

var date = new Date();
var timestamp = date.getTime();
$.ajax({
  type: "GET",
  url: "static/main.xml?="+timestamp
})

Answer 3

It looks like you're updating the values of the variables on a successful request callback, however your code to update the text representation is being called outside the AJAX function. This means that when the function is called, the AJAX request is made and the DOM is being updated before the request has finished. You need to move your DOM update logic into the success handler of $.ajax after updating the variables.

It appears you're getting a cached response. You should use cache: false in your request options, but I would also recommend removing the async: false option as well since you're using callbacks to update the variables' values anyway. Here's the updated code:

//AJAX XML file parsing
function pull_data(){

//Gather Data from main.xml and store into variables
$.ajax({
    type: "GET",
    url: "static/main.xml",
    async: false,
    success: function(xml){
        $(xml).find('item').each(function(){
            var id = $(this).find('id').text();
            switch(id){
                case "ftemp_data":
                    f_temp = $(this).find('value').text();
                    break;
                case "stemp_data":
                    s_temp = $(this).find('value').text();
                    break;
                case "fuel_level_data":
                    fuel_level = $(this).find('value').text();
                    break;
                case "humidity_data":
                    humidity = $(this).find('value').text();
                    break;
                case "blower_speed":
                    alert("Changing bspeed");
                    bspeed_data = $(this).find('value').text();
            }
        });
        alert("Pull Success "+ bspeed_data);

        //Request was successful, populate HTML with variables
        $("#ftemp_data").text(f_temp+("\u00B0"));
        $("#stemp_data").text(s_temp+("\u00B0"));
        $("#fuel_level_data").text(fuel_level+"%");
        $("#humidity_data").text(humidity+"%");
        $("#bspeed_data").text(bspeed_data);
    },
    error: function(data){
        alert("AJAX failed: "+ data.status + ' ' + data.statusText);
    }
});
}