For purpose of this post i created a simple example:
http://wagoon.demoeshop.net/test-remove-vue.html
In this example you will find two buttons.
First button creates DIV element, then creates a Vue app and mount it to that div
Second button will unmout the app
Example code
In my example, you will find two buttons
<button type="button" onclick="myTest.mount()">.mount()</button>
<button type="button" onclick="myTest.unmount()">.unmount()</button>
Vue.js 3 is included
<script src="https://unpkg.com/vue#next"></script>
Whole javascript code is wrapped in function testClass() for debugging reasons:
function testClass(){
// vueApp is public just for debugging reasons
this.vueApp = null;
// creates DIV with id #appDiv and apends it to <body>
function createDiv(){
var div = document.createElement('div');
div.id = "appDiv";
document.body.append(div);
}
// creates new Vue app and mounts it to #appDiv
this.mount = function(){
createDiv();
this.vueApp = Vue.createApp({"template":"Vue mounted"});
this.vueApp.mount('#appDiv');
}
// unmounts Vue app
this.unmount = function(){
// MEMORY LEAK HERE:
this.vueApp.unmount('#appDiv'); // this line should mark vueApp as collectable for garbage collector,it's not
this.vueApp = null; // event this line does not help
// SOLUTION: only removing app taget element from DOM is marking object created with Vue.createApp()
// as collectable by garbage collector.
// document.querySelector('#appDiv').remove();
}
}
myTest = new testClass();
How to find memory leak in google chrome console:
For debugging reason, created app is stored to this.vueApp in testClass so we can find the object id easily. Just follow these steps
Run the code
click on first button (.mount Vue app). "Vue mounted" text will appear
open chrome console and switch to Memory tab
Take a heap snapshot
click on second button (.unmount Vue app). "Vue mounted" text will disappear
back on the Memory tab click on "Collect garbage" (icon with dustbin)
Take second heap snapshot
Switch to first taken snapshot and filter "testClass". (you will see only one result). Open it and find public property "vueApp". Next to it you will find #ID of object stored in this property (for example #567005)
Switch to second snapshot and press CTRL+F (find). Search for the same #ID (for example #567005). Here is memory leak: object created with Vue.createApp is still in memory! It was NOT collected with garbage collector, because something is still pointing to this object
How to solve this memory leak
Only solution I found is removing DIV#appDiv from the DOM (code for removing this element is commented in the myTest.unmount() method). After that, calling garbage collector again will remove this object from memory.
Is there any other solution?
Why is this (big) problem
In big apps with multiple screens, creating and deleting whole app is the only way, how to save memory (script just loads code for actual page, and when user wants another page, actual page is destroyed and new page is loaded, then new Vue app is created)
You can't also solve this problem with creating dynamic components, because Vue3 removed (and i thing its big mistake) the $destroy method, so when you create new component for new screen, the old component will remain in memory forever.
Vue router will not solve this problem, because Vue router loads all pages on start and that is not acceptable in big apps, because the network bandwidth will be huge (megabytes of code loaded for just one app is just wrong)
Fixed in VUE 3.0.6
VUE js version 3.0.6 fixed this problem
Related
I am passing an element ID using the location hash like so:
https://example.com/object/id#sub-object
However, the list of sub-object elements is loaded dynamically from an api after page load.
How can I scroll the viewport to the given element once the async request completes? Given that it's location is not available in the DOM on page load.
I solved this myself, I used jquery for the scroll animation because, easy.
if(window.location.hash && !this.hasScrolled){
var hash = location.hash.substring(1);
$('html, body').animate({scrollTop: this.$refs[hash][0].offsetTop -200} ,800);
this.hasScrolled = true;
}
This had to happen in the updated() hook on the component as this is the point when the element's offset is known. I added a hasScrolled property (initially set to false) so I can make sure it only does the scroll on initial page load.
I'm having trouble understanding how data-binding works now.
On my index page I've got an object (obtained as JSON from a RESTful service), which works just fine when applied to a custom element like:
<main-menu class="tiles-container ofvertical flex layout horizontal start"
menuitems="{{menuitems}}">
</main-menu>
var maintemplate = document.querySelector('#fulltemplate');
maintemplate.menuitems = JSON.parse(data.GetDesktopResult);
This works as expected, and when I load my page with different users, main-menu changes as it should to show each user's desktop configuration. (This menuitems object reflects position and size of each desktop module for each user).
Now, users used to be able to change their configuration on the go, and on Polymer 0.5 I had no problem with that, just changed my maintemplate.menuitems object and that was that, it was reflected on the template instantly.
As I migrated to Polymer 1.0, I realized changes on an object wouldn't change anything visible, it's much more complicated than this, but just doing this doesn't work:
<paper-icon-button id="iconback" icon="favorite" onClick="testing()"></paper-icon-button>
function testing(){
debugger;
maintemplate = document.querySelector('#fulltemplate');
maintemplate.menuitems[0][0].ModuleSize = 'smamodule';
}
The object changes but nothing happens on the screen until I save it to DB and reload the page.
Am I missing something /Do I need to do something else on Polymer 1.0 to have elements update when I change an object passed as a property?
Before you ask, I've got those properties setted as notify: true, it was the inly thing I found different, but still doesn't work
Thanks for reading!
EDIT:
this is the code menuitems is used in:
<template is="dom-repeat" items="{{menuitems}}" as="poscol">
<div class="positioncolum horizontal layout wrap flex">
<template is="dom-repeat" items="{{poscol}}" as="mitem" index-as="j">
<main-menu-item class$="{{setitemclass(mitem)}}"
mitem="{{mitem}}"
index="{{mitem.TotalOrder}}"
on-click="itemclick"
id$="{{setitemid(index, j)}}">
</main-menu-item>
</template>
</div>
</template>
main-menu-item is just set of divs which changes size and color based on this object properties
You need to use the mutation helper functions if you want to modify elements inside an object or array otherwise dom-repeat won't be notified about the changes (check the docs):
function testing(){
debugger;
maintemplate = document.querySelector('#fulltemplate');
this.set('maintemplate.0.0.ModuleSize', 'smamodule');
}
I have a WinJS application (a Windows 8.1 app using HTML/JS, not C#/XAML).
I've implemented a custom navbar in my default.html, with some buttons that have click event listeners attached to them. Each handler calls nav.navigate() with the url of the page corresponding to the nav button.
One of my pages (call it /pages/myPage/myPage.html) has several buttons on it. Each button has a click event listener bound to it in the page's ready function. This works fine when navigating between several pages.
However, if I'm on myPage (with working button click handlers) and click the navbar button for myPage again, the page looks like it reloads. The ready function seems to be called (i.e. it console.log statements in it are executed), but the buttons on the page seem to completely lose their click handlers!
If I navigate to another page, then navigate back, the buttons work fine again. But no matter what I do, "reloading" the page by navigating to itself (nav.navigate("/pages/myPage/myPage.html") while on myPage) causes my click handlers to be lost.
Why does this happen? My ready function is called, but somehow the click handlers are never re-attached.
Here's what the ready function for myPage looks like:
ready: function (element, options) {
document.getElementById("myButton").addEventListener("click", this.myButtonClicked);
},
Here's what the click event listener for the myPage nav button looks like (this code is in default.js):
myPageNavButton.addEventListener("click", function () {
nav.navigate('/pages/myPage/myPage.html');
});
Page nav in WinJS is just a matter of DOM replacement. When you do a nav, the target “page” contents are loaded into the DOM and then the previous “page’s” contents are unloaded. You can see this in navigator.js in the _navigating method. It creates a new element for the page being loaded, renders that fragment therein, and then unloads the old page.
The ready method for the new page, however, is called before the old page is unloaded (this was a change in WinJS 2.0, as WinJS 1.0 unloaded the old page before calling ready). The upshot of this is that when you navigate to the same page that’s already loaded, myPage.html(A) is in the DOM when you load myPage.html(B). When you execute the code in your ready method, then, getElementById will find the buttons in myPage.html(A) and so you're attaching handlers to that element. But then after you return from ready, myPage.html(A) is unloaded, so you lose the handlers. And because you never attached handlers to the buttons in myPage.html(B), they're just inert.
So what can you do about it? The best solution, in my mind, is to avoid navigating to the same page in the first place, because it's just fraught with other peril in the long run. To do this, wrap your call to nav.navigate with a check for whether you're already on the target page. Here's an implementation of a function that does that:
function navigateIfDifferent(target) {
var page = document.getElementById("contenthost").winControl.pageControl;
var fullTarget = "ms-appx://" + Windows.ApplicationModel.Package.current.id.name + target;
if (fullTarget !== page.uri) {
WinJS.Navigation.navigate(target);
}
}
This assumes that the PageControlNavigator control that you're using is in a div called "contenthost" in default.html (which is what the VS template gives you). What I'm then doing is building the full in-package URI for the target page and comparing that to the uri of the current page control, which is also a full in-package URI. You could also strip off the ms-appx:// part from the current page URI and compare to the target URI. Either way.
Anyway, with this function, replace your calls to nav.navigate with navigateIfDifferent, and you should be good.
I use Durandal 2.0 & Breeze in my SPA.
I have a sidebar menu for my drivers (Chauffeurs) where user can click on submenus (Récents, Disponibles, Indisponibles) for calling my view with different parameters. This will fill a koGrid with data. The data is fetched in the activate call and the binding of the koGrid is done in the compositionComplete.
Everything goes well most of the time. Things goes wrong when I click very quickly on submenus (calling the same view). Example: I click on 'Récents' and immediately (without waiting for the view to display) I click on 'Disponibles'.
I have the following for the activate:
var activate = function (filterParam) {
filter(filterParam);
pagedDataSource.getDataFunction = getData;
pagedDataSource.getPredicatesFunction = getPredicates;
return pagedDataSource.reload();
};
And I have the following code for the compositionComplete:
var compositionComplete = function (view) {
bindEventToList(view, '.kgCellText', gotoDetails);
$('#mySearchGrid').attr('data-bind', 'koGrid: gridOptions');
ko.applyBindings(vm, document.getElementById('mySearchGrid'));
};
When I trace the activity, I noted that if user click quickly on submenus, the activate does not have the time to finish and is called again (for the second click of the user) and the compositionComplete does not execute. Then after that, nothing more happened visually. It seems blocked.
Any idea how can I prevent this problem?
Thanks.
The migration to the latest Durandal version 2.0.1 fixed the problem.
Let's say in a view I have a DojoX Mobile ListItem that is pulling an HTML view fragment into the DOM via AJAX and then transitioning to that view. Assume this is all working fine.
Now, I go back to the initial view that had that ListItem on it and click some other button that destroys that view node from the DOM. If I now click on that ListItem that previously loaded that view node into the DOM (which has now been removed), it will try to transition to a view that doesn't exist. It doesn't know that it has been removed.
Is there some type of way to tell a ListItem that it needs to fetch the HTML again because what was previously fetched no longer exists? I am not seeing anything about doing this in any documentation anywhere. I don't think a code sample is really necessary here, but I can provide a minimal one if necessary.
I went a different route and left the view exist in the DOM, and simply made a function that clears all sensitive data out of the view.
Okay, in this case, i guess you could hook the onShow function of your ListItem container(or any other onchange event). Create a listener for said handle to evaluate if your item needs reloading. Following is under the assumtion that it is the item.onclick contents showing - and not the label of your item which contains these informations
Or better yet, do all this during initialization so that your ListItem container will be an extended with custom onClick code.
Seems simple but may introduce some quirks, where/when/if you programatically change to this item, however here goes:
function checkItem() {
// figure out if DOM is present and if it should be
if( isLoggedIn() ) {
this.getChildren().forEach(function(listitem) {
if( dojo.query("#ID_TO_LOOK_FOR", listitem.domNode).length == 0 ) {
// this references the listItem, refresh contents.
// Note: this expects the listitem to be stateful, have no testing environment at time being but it should be
listitem.set("url", listitem.url);
}
});
}
}
Preferably, set this in your construct of the container for your ListItems
var listItemParent = new dojox.mobile.RoundRectList({
onShow : checkItem,
...
});
Or create listener
var listItemParent = dijit.byId('itemRegistryId');
// override onClick - calling inheritance chain once done
dojo.connect(listItemParent, "onClick", listItemParent, checkItem);