"Multiple instances of JavaScript files seem to be present when using Ajax navigation

Question

"Multiple instances of JavaScript files seem to be present when using Ajax navigation

Having some difficulties with AJAX navigation. The issue is that the JavaScript files loaded remain in the browser even after the new content is loaded, even when they are no longer in the DOM. These files appear as VM files in the browser console and continue to execute their code. This is not desired behavior as the JavaScript file should be replaced when new content is fetched via AJAX.

The structure of my DOM looks like this:

<body>
    <header></header>

    <main id="contentToBeReplaced">

        <p>New content with its own JS</p>
        <script>
            var script = "js/new.js";
            $.getScript(script);
        </script>
    </main>

    <footer></footer>

    <script src="js/main.js"></script>
</body>

Each time a page loads with its respective JavaScript file, a new VM file appears and retains all the older ones, causing issues:
https://i.stack.imgur.com/iNJFv.png

What could be causing this problem and how can it be resolved? I need to prevent duplicate files and remove the existing JavaScript file when a new one is loaded.

javascript jquery ajax browser duplicates

Answer 1

Answer №1

Every unique entry within the Javascript global execution context is able to represent either a single object or variable. When the same function is repeatedly loaded into the global context, it replaces the function code each time.

It's important to ensure that scripts being lazy-loaded are managed in a way that they correspond to the same entry within your global context (or framework).

Take a look at the following sample JavaScript codes that are assumed to be lazy-loaded at two different times:

// Script 1

var dynFun = function() {
                console.log('Loaded early');
             {

// Script 2
var dynFun = function() {
                console.log('Loaded late');
             {

If you load script one and execute dynFun(), it will output "Loaded early". Then, if you load the second script and run dynFun() again, it will display "Loaded late".

However, if these functions involve automatic processes like setTimeout, they will continue to operate until the page is closed.

In such cases, dynamic scripts should first perform some cleanup:

var timeTracker; // This is a global variable

var dynFun = function() {
                  if (timeTracker)
                      clearTimeout(timeTracker)

                   timeTracker = setTimeout(someFn, 1000)   
             {

Keep in mind - in garbage-collected languages like JS, you cannot directly deallocate memory. You can only manipulate references to objects to trick the clean-up process.

Answer 2

Every unique entry within the Javascript global execution context is able to represent either a single object or variable. When the same function is repeatedly loaded into the global context, it replaces the function code each time.

It's important to ensure that scripts being lazy-loaded are managed in a way that they correspond to the same entry within your global context (or framework).

Take a look at the following sample JavaScript codes that are assumed to be lazy-loaded at two different times:

// Script 1

var dynFun = function() {
                console.log('Loaded early');
             {

// Script 2
var dynFun = function() {
                console.log('Loaded late');
             {

If you load script one and execute dynFun(), it will output "Loaded early". Then, if you load the second script and run dynFun() again, it will display "Loaded late".

However, if these functions involve automatic processes like setTimeout, they will continue to operate until the page is closed.

In such cases, dynamic scripts should first perform some cleanup:

var timeTracker; // This is a global variable

var dynFun = function() {
                  if (timeTracker)
                      clearTimeout(timeTracker)

                   timeTracker = setTimeout(someFn, 1000)   
             {

Keep in mind - in garbage-collected languages like JS, you cannot directly deallocate memory. You can only manipulate references to objects to trick the clean-up process.

Answer 3

Answer №2

Through extensive research, I managed to successfully resolve the issue at hand. To my knowledge, there is no foolproof method to "unload" javascript files without having to refresh the page or manually clear the browser's memory cache.
Most of the code within these dynamic javascript files pertains to event functions, so I opted to bind events to the document rather than each individual element using the following syntax:

$(document).on("click", "#myElement", function () {

});

Consequently, every time the javascript file was loaded, the events were repeatedly bound and executed multiple times from the VM files. When an element is removed from the DOM, its bound event is also removed unless it is bound to the document like in my case. Thus, I modified the on() method to directly bind the event to the element:

$("#myElement").on("click", function() {

});

This adjustment effectively resolved my issue as the HTML portion replaced with AJAX removes those elements along with their associated events, eliminating the necessity for utilizing off() to manually remove the bound events. Moreover, essential functions that are meant to be executed across multiple pages should be housed in the main js script.
Nevertheless, @CharlieH raises a valid point in his response.

Answer 4

Through extensive research, I managed to successfully resolve the issue at hand. To my knowledge, there is no foolproof method to "unload" javascript files without having to refresh the page or manually clear the browser's memory cache.
Most of the code within these dynamic javascript files pertains to event functions, so I opted to bind events to the document rather than each individual element using the following syntax:

$(document).on("click", "#myElement", function () {

});

Consequently, every time the javascript file was loaded, the events were repeatedly bound and executed multiple times from the VM files. When an element is removed from the DOM, its bound event is also removed unless it is bound to the document like in my case. Thus, I modified the on() method to directly bind the event to the element:

$("#myElement").on("click", function() {

});

This adjustment effectively resolved my issue as the HTML portion replaced with AJAX removes those elements along with their associated events, eliminating the necessity for utilizing off() to manually remove the bound events. Moreover, essential functions that are meant to be executed across multiple pages should be housed in the main js script.
Nevertheless, @CharlieH raises a valid point in his response.

Answer 5

Answer №3

To ensure that the "new.js" file can be tracked in Chrome Dev Tools, include the following line at the beginning of the file:

//# sourceURL=new.js

Answer 6

To ensure that the "new.js" file can be tracked in Chrome Dev Tools, include the following line at the beginning of the file:

//# sourceURL=new.js

Answer 7

Answer №4

To enhance the security of your JavaScript code, consider including 'use strict'; at the beginning of your file. This will activate a stricter parsing mode that helps prevent unintentional global variables. If you're still facing issues, check out this informative article on "garbage collector" and learn more about preventing memory leaks in JavaScript: "4 Types of Memory Leaks in JavaScript and How to Get Rid Of Them"

Answer 8

To enhance the security of your JavaScript code, consider including 'use strict'; at the beginning of your file. This will activate a stricter parsing mode that helps prevent unintentional global variables. If you're still facing issues, check out this informative article on "garbage collector" and learn more about preventing memory leaks in JavaScript: "4 Types of Memory Leaks in JavaScript and How to Get Rid Of Them"

"Multiple instances of JavaScript files seem to be present when using Ajax navigation

Answer №1

Answer №2

Answer №3

Answer №4

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