Triggering CSS Transitions on Appended Elements

CSS transitions on newly-appended elements can fail to trigger due to browser optimizations that batch reflows. When both the addition of the element and the CSS transition are executed in a single JavaScript round, the browser may combine these operations, resulting in only a single style value being applied without any intermediate transition.

Methods for Triggering Transitions

Multiple methods exist to trigger CSS transitions on appended elements:

• SetTimeout: Delaying the addition of the CSS class using setTimeout() allows for two style values to exist before rendering, triggering the transition.
• offsetWidth: Accessing an element's offsetWidth property forces a reflow, ensuring that the CSS transitions are applied.
• **getComputedStyle(): Similar to offsetWidth, calling getComputedStyle() also triggers a reflow and forces the transition.

Preferred Solution

The preferred solution for triggering CSS transitions on appended elements is accessing the element's calculated style properties using offsetWidth or getComputedStyle(). This approach ensures that transitions are triggered consistently and minimizes the risk of interrupted animations due to browser optimizations.