When using jQuery, adding a class does not always trigger CSS animation

Question

When using jQuery, adding a class does not always trigger CSS animation

Currently facing a peculiar issue. I am utilizing jQuery to load articles from JSON and would like to dynamically add a class of 'animate' to each loaded element.

$.each(jsonArticles, function (i, article) {

    var $articleHTML = $(
    '<article class="article">' +
        '<a href="' + jsonObject.filmLink + article.reviewLink + '"><img src="' + jsonObject.imagePath + article.reviewImage + '" alt=""></a>' +
        '<h1><a href="' + jsonObject.filmLink + article.reviewLink + '">' + article.reviewTitle + '</a></h1>' +
        '<p><a href="' + jsonObject.filmLink + article.reviewLink + '">' + article.reviewSummary + '</a></p>' +
    '</article>');

    $articles
        .append($articleHTML)
            .find("article")
                .addClass("animate");

});

The addition of the class works well as verified in Firebug where it shows up for each article tag.

However, when attempting to apply a CSS transition to animate the class added to the article, there is no animation and it instantly switches to the final style (opacity: 1).

.article { 

opacity: 0;

    -webkit-transition: all 0.5s ease;
    -moz-transition: all 0.5s ease;
    -o-transition: all 0.5s ease;
    transition: all 0.5s ease;

}

.article.animate { 

    opacity: 1;

}

The expected animation does not occur despite the class being added and successfully setting the article to opacity: 1. It appears abruptly.

If the .animate class is modified to include a :hover, then the articles will only appear on hovering with the animation working as intended. This inconsistency between immediate addition and hover effects is puzzling.

.article.animate:hover { 

    opacity: 1;

}

Your insights on this matter are highly appreciated.

Thank you, Mikey.

Live Demo: http://jsfiddle.net/Pz5CD/ Observe how the articles abruptly display at full opacity without any animation.

javascript jquery css css-animations

Answer 1

Answer №1

Important Update:

Upon further examination, it has been discovered that the original poster (OP) actually desires a sequential fading effect for each element, which goes beyond the initial query. Nevertheless, I will retain my response to address the initial question.

Challenge with CSS Animations not Triggering on addClass in jQuery

The root cause of the issue lies in the fact that the new HTML content is inserted into the page and the `animate` class is added before the corresponding CSS styles are fully applied. To optimize performance, browsers tend to skip ahead in such scenarios. For instance, if you were to repeatedly add and remove a class multiple times consecutively, there would be no visible change as the browser would simply jump to the final outcome. Therefore, to ensure proper execution, you need to force a redraw on the element so that all preceding styles can take effect before adding the class. Below is a function that addresses this issue and should work reliably across various browsers, although the behavior of a reDraw cannot be guaranteed. Nevertheless, it typically functions as intended and offers a useful solution!

Check out the live demo here (click). You can observe the impact of the reDraw by commenting it out and solely leaving the `addClass()` function.

$('body').append($articleHTML);
$a = $('body').find("article");
reDraw($a).then(function() {
  $a.addClass("animate");
});

function reDraw($element) {
  var deferred = new $.Deferred();
  setTimeout(function() {
    var h = $element[0].offsetHeight;
    var s = $element[0].getComputedStyle;
    deferred.resolve();
  }, 0);
  return deferred.promise();
}

The most effective method to trigger a redraw is by accessing either the `offsetHeight` or `getComputedStyle` of an element. However, in some instances, these methods may fail to induce a redraw on specific mobile devices. To reinforce the redraw process, I have included a `setTimeout` as well. Even a minimal timeout value of 0 will suffice, but to maintain the call stack order, I utilize a promise to ensure that the subsequent operation (adding your class) occurs post-redraw. This necessitates using the syntax exemplified above to incorporate the class - `redraw($element).then(function() { //your code`.

As a fun exercise, I created a demonstration showcasing class transitions with and without reDraw for comparison. Experience it here: http://jsbin.com/EjArIrik/1/edit

Answer 2

Important Update:

Upon further examination, it has been discovered that the original poster (OP) actually desires a sequential fading effect for each element, which goes beyond the initial query. Nevertheless, I will retain my response to address the initial question.

Challenge with CSS Animations not Triggering on addClass in jQuery

The root cause of the issue lies in the fact that the new HTML content is inserted into the page and the `animate` class is added before the corresponding CSS styles are fully applied. To optimize performance, browsers tend to skip ahead in such scenarios. For instance, if you were to repeatedly add and remove a class multiple times consecutively, there would be no visible change as the browser would simply jump to the final outcome. Therefore, to ensure proper execution, you need to force a redraw on the element so that all preceding styles can take effect before adding the class. Below is a function that addresses this issue and should work reliably across various browsers, although the behavior of a reDraw cannot be guaranteed. Nevertheless, it typically functions as intended and offers a useful solution!

Check out the live demo here (click). You can observe the impact of the reDraw by commenting it out and solely leaving the `addClass()` function.

$('body').append($articleHTML);
$a = $('body').find("article");
reDraw($a).then(function() {
  $a.addClass("animate");
});

function reDraw($element) {
  var deferred = new $.Deferred();
  setTimeout(function() {
    var h = $element[0].offsetHeight;
    var s = $element[0].getComputedStyle;
    deferred.resolve();
  }, 0);
  return deferred.promise();
}

The most effective method to trigger a redraw is by accessing either the `offsetHeight` or `getComputedStyle` of an element. However, in some instances, these methods may fail to induce a redraw on specific mobile devices. To reinforce the redraw process, I have included a `setTimeout` as well. Even a minimal timeout value of 0 will suffice, but to maintain the call stack order, I utilize a promise to ensure that the subsequent operation (adding your class) occurs post-redraw. This necessitates using the syntax exemplified above to incorporate the class - `redraw($element).then(function() { //your code`.

As a fun exercise, I created a demonstration showcasing class transitions with and without reDraw for comparison. Experience it here: http://jsbin.com/EjArIrik/1/edit

Answer 3

Answer №2

In order to apply the class to the element once it has been displayed on the screen, consider using a setTimeout function

setTimeout(function(){
    $articleHTML.addClass("animate");
}, index * 500 );

http://jsfiddle.net/Pz5CD/1/

Answer 4

In order to apply the class to the element once it has been displayed on the screen, consider using a setTimeout function

setTimeout(function(){
    $articleHTML.addClass("animate");
}, index * 500 );

http://jsfiddle.net/Pz5CD/1/

When using jQuery, adding a class does not always trigger CSS animation

Answer №1

Important Update:

Challenge with CSS Animations not Triggering on addClass in jQuery

Answer №2

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