Javascript removeChild() and appendChild() VS display=none and display=block|inline - javascript

I'm developing a web application that shows some controls and descriptions dynamically (I don't want to use jQuery or other libraries).
At this moment i make appear and disappear controls using:
element.setAttribute("style", "display : inline");
and
element.setAttribute("style", "display : none");
but i'm thinking about using:
element.appendChild(childRef);
and
element.removeChild(childRef);
So, which one is the best solution in terms of system speed and elegance of the code?
Or is there a better way to go about this?

element.appendChild(childRef); and element.removeChild(childRef); both make the browser to manipulate the DOM tree while changing CSS just changes one of the attributes.
So, changing CSS is faster.
Dev Opera says
When an element has its display style set to none, it will not need to repaint, even if its contents are changed, since it is not being displayed. This can be used as an advantage. If several changes need to be made to an element or its contents, and it is not possible to combine these changes into a single repaint, the element can be set to display:none, the changes can be made, then the element can be set back to its normal display.
This will trigger two extra reflows, once when the element is hidden, and once when it is made to appear again, but the overall effect can be much faster
Another relevant article explains about reflow and repaint

Definitely go on using display properties.
They are much faster than removing/appending children, but most important they work very well in every browsers.
I know appendChild/removeChild are supposed to be well supported in IE, but sometimes on my IE7 a still get things moving around after a new element is appended (this is only my personal experience).
Regarding the way you change the display properties I would simply do a more easy and cross-browser (setAttribute is not well supported by IE6/7 an also IE8 when in IE7 mode):
element.style.display = 'none'; //for hiding an element
element.style.display = ''; //for showing that element again using its default way of displaying
Showing an element by using display = 'inline' is wrong because the element might have by default a display block way of showing like DIV tags and you are changing its way of showing to inline wich is not correct and might lead to elements in your page moving out from the places you expect them to be.

I doubt there's much in it one way or the other, and even if there is, I bet it varies by implementation (IE vs. Chrome vs. Firefox vs. ...). Both will cause reflow events in the tree.
Showing and hiding is simple and straightforward. Adding and removing can have its uses, but for the most part is probably overkill. For one thing, you have to keep a reference to it so you can add it back later, and you have to remember where you need to add it back.
But (and this is a bit off-topic) your mechanism for showing and hiding has some issues:
With your example code, things can only be inline, not inline-block or block, which would be somewhat...limiting.
Your code also completely replaces the style information on the element (and may not work on IE; see David's comment on your question), so all other styles directly applied to the element will get blown away; consider using the style property of the element instead: childRef.style.display = 'none"; and childRef.style.display = "inline"; (or block, or...). That way, you don't bludgeon any other styles on the element.
Completely removing a child from the tree (while keeping a reference to it so you can put it back later) definitely has its uses, though. For instance, when it's not in the tree, it won't be found when you're walking the tree with selectors for doing this, that, and the other; which may be helpful.

A small aside: if you happen to be dealing with user editable elements in IE (i.e. inside a document with designMode "on" or inside an element with contenteditable true), setting the CSS display property to none won't have any effect, and you'll need to remove the elements from the DOM to hide them.

The first approach is better i think which just hides and displayes but does not remove from the DOM and add again.

I would think that performance is better just updating the style.
The answer will depend on what you are using the elements for. If it is very dynamic whether they should be shown or not, it might be a solution to add/remove from DOM, but if there are a static set of elements, it might be easier to set the style. Setting the style, you also have more control of the position in the document. Adding/removing from DOM, you need to be sure it is added at the right place.
Note:
Instead of element.setAttribute("style", "display:none"); you can use element.style.display= "none"; If you use the first approach, you will remove any other style settings on the element.

I think editing the style of an element will be faster, but which is better hide the element or remove it from dom, this depends on your needs, if you need to just hide the element or remove it.
May be you don't need the user see the element but you need to do some js logic on it, so hide here will be the best.

Related

JS : How to get notified after insertBefore()?

Is there a way to get notified, after inserting an element into the DOM with insertBefore(), when this element becomes actually visible/available to user ? Especially to start applying CSS transforms on it ?
Complete problem
Forgive me if this question is recurrent, I didn't find a suitable answer so far. I'm trying to implement a custom popup dialog system on a website of my own, similar to SweetAlert or some other products.
I would like to apply some special effects when this popup shows up, such as a progressive darkening of the background, as well as a slow vertical motion on the box itself.
To achieve all of this, I spawn one big, fixed div element covering the whole screen (the background) and containing the popup box. When I need it, I first insert this element as body's first child, tagging it with a special invisible class. Once inserted, I remove this invisible class from the element and let the CSS rules do the magic.
The problem is that even if removed the class after having inserted this element, this one will be rendered only when the Javascript function leaves, hence directly in its final state.
When doing this on a complete initial page, the load event helps. I now would like to do the same on an existing page.
As always, I'm interested on both solutions to this (potentially XY) problem: if there's a better way to do it, I'll be happy to discover it, but I'm still interested in solving this particular situation anyway.
Thanks in advance to everyone.
EDIT: currently performing tests on Firefox 82.0.2
Thanks to comments above, here's a valid solution to both exposed problems:
"Mutation Observer", as well as former "Mutation Events" (now deprecated) are the best way to get notified when something is inserted. It won't help with animations issues, though, because it's still not guaranteed to be rendered yet at this time ;
Rather than applying a class then another to perform a transition, it's better to define a regular animation using #keyframes that plays only once. It's guaranteed to be played when the object appears, by definition.
Many thanks to "Pomax", F4st3r and epascarello for their help.

is it possible to view one html element twice on the same page, or must I create a duplicate?

I am creating a site that allows viewing and editing the contents of the 'src-div' contents within the 'edit-div.' I am not editing the src-div directly, because its thumbnailed using css zoom property.
I have considered using knockout.js to bind both elements to an observable. Currently, I have implemented the feature with jquery .html() function: simply set edit-div innerhtml to src-div innerhtml on 'select', and reverse the process after changes are made to edit-div to update the src-div.
I am wondering if I really need 2 divs here, or if there is some way to actually view the same element twice on a page, and any changes made will automatically reflect in both 'views,' elimiating the need to copy innerhtml property back and forth between two elements.
essentially, this is like a mirror effect, without the flip.
the closest thing I found so far is:
http://developer.apple.com/library/safari/#documentation/InternetWeb/Conceptual/SafariVisualEffectsProgGuide/Reflections/Reflections.html
Any recommended practices for performing this task are appreciated.
(Almost) everything you see on a page has a counterpart in the DOM. Everything in the DOM gets exactly rendered one time (apart from pseudo-classes). And every node in the DOM can only have one parent (no exclusions).
Unfortunately you'll have to clone the specific node and add changes to both, as there is no copy & translate mechanism in the current CSS documentation.
If you're using jquery you can use one div and "clone" it. You can read this for more information.
http://api.jquery.com/clone/
If you set the class of the div to the same thing, you can have changes propagated to both. Then you can apply .addClass to the second div to apply a "reflected" affect (if that's your final goal).

In JavaScript what is the right way to kill a DOM element?

I know that I can set it's style to "display: none"
However, that just hides it.
I really want to kill a DOM element and all of it's children.
The context is that I'm building a desktop-like GUI system (for learning purposes) inside of a DOM, and when a "window" is closed, I want that DIV and all it's children to be removed.
Thus, in JavaScript, how to I tell the GC "hey, get rid of this DOM element, it's no longer needed"?
Thanks!
To remove all elements, I suppose you could set element.innerHTML to an empty string (although I've never tried it myself). Otherwise, you could use element.removeChild(child), as described here.
jQuery also supports $([selector]).remove([selector]), which is more flexible in specifying which elements you want to remove at once. There's more information about jQuery remove here.
What about removeChild ?
See http://dustindiaz.com/add-and-remove-html-elements-dynamically-with-javascript/ for more information

Javascript: Best approach for displaying one element of a list

What is the better approach?
adding multiple DOM elements to a parent node and setting all of them but one to "hidden" (disply='none'). On demand set the currently visible element to "hidden" and another one to "visible".
Just add one DOM element and on demand change its attributes and content.
Definitely option 1. Messing around with the DOM is never a good idea. We just all do it out of necessity.
The less you change the DOM, the better.
P.S. remember to cache your selectors...

Using jquery to add/remove class but elements are not redrawn to reflect

I have two elements (think of two buttons side by side). I dynamically toggle the class "focusd" to change the highlighted effect. However, there's a quirk it doesn't always get redrawn and/or inserted in the DOM. For example, if in chrome I do console.log, I see the class changes (I'm using removeClass/addClass in jquery). But if I go to the Elements tab in the inspector, it shows the classes from before (and in fact, I'm not seeing the redrawing reflecting the toggling of the classes.)
I tried setting the parent div to display none then back to block but that didn't work. It's a "one off" modale screen, so efficiency doesn't matter so I've resorted to this hack where I essentially copy the parent's innerhtml, remove and reinsert the element. Horrible!
// Not sure why I need this hack. But if I don't, the buttons don't seem to get redrawn
var htm = jQuery(".rdata_container").html(); // copy the innerhtml
jQuery(".rdata_container").empty(); // empty and then append back
jQuery(".rdata_container").append(htm);
This seems like a specific quirk that someone must have ran into (I hope). If so, I'd love to know why my changes aren't reflected.
EDIT
Code posted here:
http://jsfiddle.net/roblevintennis/JCZnf/
you can use setTimeout when you are doing the other operation on the element, so for example:
$elm.addClass('hide')
setTimeout(function(){
$elm.removeCalss('hide')
},0);
Or you could force a repaint like so:
$elm.addClass('hide')
$elm.scrollTop; // forces a repaint (might be expensive for large amount of items)
$elm.removeCalss('hide');
These tricks will force the browser to re-draw the change, because there are two things happening here and the browser logic just combines them into one, which isn't the desired behavior.
Not directly an answer to your question, but you can use jQuery's toggleClass function to simplify your code.
Here's an updated version that uses toggleClass() and jQuery 1.6 and AFAICT works fine.
http://jsfiddle.net/JCZnf/7/

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