Why Aren\'t My CSS Transitions Triggering From JavaScript?

CSS Transitions not Triggering from JavaScript

When applying CSS3 transitions to elements through JavaScript, it's crucial to understand the mechanics of transition activation. To make transitions effective, three essential steps must be followed:

1. Define Transitionable Properties:
Ensure that the element has the transitionable property explicitly specified. In this case, opacity should be set to opacity: 0.

2. Specify Transition Effect:
Define the transition effect using the transition property, e.g., transition: opacity 2s.

3. Update Transitionable Property:
To trigger the transition, the transitionable property must be updated, e.g., opacity: 1.

Resolving the Issue with JavaScript Transitions:
As per the provided code example, the issue arises because the browser cannot process the property changes instantaneously when assigned through JavaScript. To resolve this, a delay is necessary to allow the browser to process the requests before applying the transitionable property. One solution is to use the window.setTimeout function to delay the assignment of the target-fadein class by 100 milliseconds.

Alternatively, you can add the target-fadein-begin class directly to the HTML, which will be parsed on page load and ensure that the transition is ready when needed. Remember, adding the transition property to an element does not trigger the animation; setting the transitionable property does.

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