safari 13.1, Supported 13.1 Source API #Īll the APIs with the Observer suffix we mentioned above share a simple API design.

It provides access to the new size of the observed elements too. It reacts to changes in size of any of the observed elements, independent of what caused the change. This is why ResizeObserver is a useful primitive. For example, appending new children, setting an element's display style to none, or similar actions can change the size of an element, its siblings, or its ancestors. This didn't even cover cases where elements change their size without the main window having been resized. If you needed the new dimensions of an element after a resize, you had to call getBoundingClientRect() or getComputedStyle(), which can cause layout thrashing if you don't take care of batching all your reads and all your writes. In the event handler, you would then have to figure out which elements have been affected by that change and call a specific routine to react appropriately. leading edge, instead of the trailing.Before ResizeObserver, you had to attach a listener to the document's resize event to get notified of any change of the viewport's dimensions. If `immediate` is passed, trigger the function on the The function will be called after it stops being called for Returns a function, that, as long as it continues to be invoked, will not Here's the basic JavaScript debounce function ( as taken from Underscore.js):

Why not limit the rate at which the function can fire? That isn't a heavy task in itself but being repeatedly fired after numerous resizes will really slow your site down. A quick example: you have a resize listener on the window which does some element dimension calculations and (possibly) repositions a few elements.

If your web app uses JavaScript to accomplish taxing tasks, a debounce function is essential to ensuring a given task doesn't fire so often that it bricks browser performance.įor those of you who don't know what a debounce function does, it limits the rate at which a function can fire. One of the biggest mistakes I see when looking to optimize existing code is the absence of the debounce function.

Javascript window resize event