perceived-performance

A filling bar reporting how far along a task is, determinate when the end is known and indeterminate when it is not.

A circular progress indicator that fills around a ring, often with the percentage in the middle.

An indeterminate loading indicator that shows work is happening without saying how much of it is left.

A container that holds a fixed width to height proportion whatever its size, so media reserves its space before it loads.

Content moving after it has already been painted, usually because something arriving late took space that was never reserved for it.

Deferring the fetch of an image, list section, or module until it is about to be needed, usually when it approaches the viewport.

Rendering only the rows currently in view and a small buffer around them, while spacers preserve the scrollbar of the full list.

A button at the end of a list that fetches and appends the next batch only when pressed, keeping the reader in control of how much arrives.

A persistent notice that the product has lost its connection, saying what still works, what is queued, and when the last sync happened.

Showing the result of an action immediately and reconciling with the server afterward, instead of making the user wait for confirmation.

Showing a cheap stand-in for an image, a blur, a dominant colour, or a low resolution copy, and swapping in the full file once it arrives.

A loading state made of grey shapes standing where the content will be, showing the layout before the data arrives.

Waiting until input has stopped for a set moment before reacting, so a burst of keystrokes or clicks produces one response instead of many.

Keeping the reader's position fixed when content loads or resizes above it, by adjusting scroll offset so the visible text does not jump.

The pause a touch browser once held before dispatching a click, kept open in case a second tap arrived and turned the gesture into a zoom.

Capping how often a continuous stream of input is acted on, so a response fires at a steady rate instead of on every event.

An animation limited to properties the compositor can handle alone, usually transform and opacity, so it keeps running even when the main thread is busy.

How many frames a second the interface actually draws, the budget every animation spends: 60fps leaves about 16ms per frame and a 120Hz display halves it.

Visible stutter in motion caused by frames arriving late or not at all, so an animation that should be continuous reads as juddering.

Reading a geometric value after writing to the DOM in the same frame, forcing the browser to lay out synchronously over and over and stalling the animation that caused it.

How long a spring appears to take, measured to the point the movement stops being visible rather than to its mathematical rest, the figure to quote against a timed animation.

The moving highlight that sweeps across placeholder shapes to signal that content is still on its way.