Mateusz Burzyński Andarist

Fix absolutely positioned divs when people turn their phones sideways

The problem

In Safari, if you have a layout container that's absolutely positioned to take up, at a minimum, its whole container (which isn't unheard of in "appey" internet home page thingies) using CSS like this:

.absolutely

A series of posts on css-in-js

0. styles as objects

First, an exercise. Can we represent all of css with plain data? Let's try.

let redText = { color: 'red' };

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent

	const {useCallback, useEffect, useReducer, useRef} = require('react');

	let effectCapture = null;

	exports.useReducerWithEmitEffect = function(reducer, initialArg, init) {
	let updateCounter = useRef(0);
	let wrappedReducer = useCallback(function(oldWrappedState, action) {
	effectCapture = [];
	try {
	let newState = reducer(oldWrappedState.state, action.action);

	function rafThrottler(callback) {
	let rafId = null;
	const flush = () => {
	callback();
	rafId = null;
	};

	return () => {
	if (rafId) {
	return;