ui-bootstrap $modal body shift fix

run.js

function measureScrollbar(document) {
	const overflowY = window.getComputedStyle(document.body).overflowY
	let scrollDiv = document.createElement('div')
	scrollDiv.className = 'modal-scrollbar-measure'
	document.body.appendChild(scrollDiv)
	const width = scrollDiv.offsetWidth - scrollDiv.clientWidth
	document.body.removeChild(scrollDiv)
	scrollDiv = null
	return {width, overflowY}
}

function hasScrollbar(target, overflowY) {
	return	overflowY === 'scroll' ||
			target.offsetHeight > window.innerHeight
}

function setPadding(target, width) {
	target.style.paddingRight = width
}

function setScrollbar(target, {width, overflowY}) {
	const bodyPad = parseInt((target.style.paddingRight || 0), 10)
	const alreadyApplied = bodyPad === width
	if (hasScrollbar(target, overflowY) && !alreadyApplied) setPadding(target, bodyPad + width)
	return alreadyApplied ? 0 : bodyPad
}

function isClassMutation(mutation) {
	return mutation.type === 'attributes' && mutation.attributeName === 'class'
}

// NOTE: https://github.com/angular-ui/bootstrap/pull/2425
export default function bodyShiftFix($window, $document, $timeout) {
	if (!('MutationObserver' in $window)) return

	$timeout(() => {
		const body = $document[0].querySelector('body')
		const measures = measureScrollbar($document[0])
		let originalPad = 0
		const observer = new MutationObserver(mutations => {
			[...mutations]
			.filter(isClassMutation)
			.forEach(({target}) => {
				if (target.classList.contains('modal-open')) {
					originalPad = setScrollbar(target, measures)
				} else {
					setPadding(target, originalPad)
				}
			})
		})
		observer.observe(body, {
			attributes: true
		})
	})
}