Interaction to Next Paint (INP)

This metric is particularly important for assessing a website or application's responsiveness, as it provides insight into how quickly the user interface updates following user input. INP measures user interactions such as mouse clicks, tapping devices with a touchscreen, and pressing on a keyboard.

A faster INP results in a more responsive and smooth user experience. To provide a good user experience, Google suggests sites should strive to have an INP of 200 milliseconds or less.

The most effective improvements include using CSS instead of JavaScript for animations, debouncing events that may be called repeatedly by user input, and reducing the DOM size so the browser doesn’t have to recalculate too many elements on each render. Other various optimization techniques are:

1. Optimize JavaScript execution: Heavy JavaScript execution can significantly impact INP. To optimize it, minimize the use of long-running tasks by breaking them into smaller chunks, use the requestAnimationFrame() method for animations, and utilize Web Workers to offload computationally expensive tasks.
2. Debounce and throttle event handlers: Debouncing and throttling can help limit the frequency of event handlers being called, reducing the workload on the main thread and improving INP. This is particularly important for events such as scrolling and resizing.
3. Use passive event listeners: Passive event listeners inform the browser that the event handler will not call preventDefault() to cancel the event. This allows the browser to optimize scroll and touch events, improving INP.
4. Optimize CSS: Heavy CSS can impact INP due to the time required for style calculations and layout. To optimize rendering performance, minimize the complexity of your CSS selectors, avoid using expensive CSS properties, and remove unused styles.
5. Prioritize visible content: Prioritize rendering the content visible on the screen (above the fold) and defer the rendering of off-screen content. This can be achieved by using techniques such as lazy loading and content placeholders.
6. Utilize virtualization: For long lists or large data sets, use virtualization libraries to render only the visible content and minimize the number of DOM elements. This reduces the workload on the browser and improves INP.
7. Optimize animations and transitions: Use the transform and opacity properties for animations and transitions, as they are less expensive for the browser to render. Avoid animating expensive properties like width, height, and margin, which can cause layout recalculations and negatively impact INP.
8. Minimize forced synchronous layout: Forced synchronous layout occurs when JavaScript reads and writes layout properties, causing the browser to recalculate the layout multiple times. Group your read-and-write operations together to minimize layout thrashing and improve INP.

These are just a couple of suggestions for optimizing your INP results. Get into a performance-first mindset with our comprehensive frontend performance checklist.

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