livewire-material/resources/js/menu.js

/**
 * `materialMenu`: the behaviour of `<x-menu>` — WAI-ARIA's menu button pattern on a popover.
 *
 * The menu button is the trigger's first button or link. Its ARIA attributes are written by
 * script, which a Livewire morph removes along with anything else the server did not render,
 * so they are written again whenever the trigger is used.
 *
 * The popover hangs on the menu button by CSS anchor positioning. The server can only name the
 * wrapper around the trigger slot, and a trigger taken out of the flow — a `position: fixed` FAB
 * in a corner of the window — leaves that wrapper behind as an empty box where the page put it,
 * so the menu opened there. Script moves the name onto the menu button, beside any name the button
 * carries itself (a button's tooltip anchors on it too), and moves it again after every morph,
 * which puts the server's attributes, and a fresh name, back.
 */
const ITEMS = '[role="menuitem"], [role="menuitemcheckbox"], [role="menuitemradio"]'

// A popover="auto" closes on the press that lands on its trigger, and the click that follows
// would open it again. A close this recent is taken as that press.
const REOPEN_GUARD_MS = 250

document.addEventListener('alpine:init', () => {
    window.Alpine.data('materialMenu', () => ({
        closedAt: -Infinity,
        anchored: null,
        returnFocus: true,
        focusWasInside: false,
        listeners: [],

        init() {
            const menu = this.$refs.menu

            this.label()
            this.anchor()

            // A morph rewrites the wrapper's style with this render's name and the button's without
            // it; the observer runs before the next frame is drawn, so an open menu never moves.
            const observer = new MutationObserver(() => this.anchor())

            observer.observe(this.$refs.trigger, { attributes: true, attributeFilter: ['style'], childList: true, subtree: true })
            this.listeners.push(() => observer.disconnect())

            // Only closes the browser starts — Escape, a press outside — arrive here alone; open()
            // and close() have already done their part, synchronously, because this event is
            // queued and a screen reader or a test reading aria-expanded in between would be told
            // the menu is shut.
            // Whether focus was in the menu is read before it closes: once closed, a browser may
            // already have handed focus to what had it before the menu opened (WebKit does, when
            // that was a focusable region around the trigger).
            this.listen(menu, 'beforetoggle', (event) => {
                this.focusWasInside = event.newState === 'closed' && menu.contains(document.activeElement)
            })

            this.listen(menu, 'toggle', (event) => {
                const opened = event.newState === 'open'

                this.control()?.setAttribute('aria-expanded', String(opened))

                if (opened) {
                    return
                }

                this.closedAt = performance.now()

                if (this.returnFocus && (this.focusWasInside || menu.contains(document.activeElement))) {
                    this.control()?.focus()
                }

                this.focusWasInside = false
            })

            // A press outside closes the menu without pulling focus back to the trigger.
            this.listen(document, 'pointerdown', (event) => {
                if (!menu.contains(event.target) && !this.$refs.trigger.contains(event.target)) {
                    this.returnFocus = false
                }
            })
        },

        control() {
            return this.$refs.trigger.querySelector('button, a[href], [tabindex]')
        },

        /**
         * Moves the anchor name the server gave the wrapper onto the menu button. The wrapper holds a
         * name only as rendered — this render's, which the popover's `position-anchor` matches — so
         * it is read there, never from the popover, which a morph may still be replacing.
         */
        anchor() {
            const trigger = this.$refs.trigger
            const control = this.control()
            const rendered = trigger.style.getPropertyValue('anchor-name').trim()
            const name = rendered.startsWith('--') ? rendered : this.anchored

            // No menu button, or an engine without anchor positioning: the wrapper keeps the name.
            if (!control || !name) {
                return
            }

            const names = control.style
                .getPropertyValue('anchor-name')
                .split(',')
                .map((each) => each.trim())
                .filter((each) => each.startsWith('--'))

            if (!names.includes(name)) {
                control.style.setProperty('anchor-name', [...names.filter((each) => each !== this.anchored), name].join(', '))
            }

            this.anchored = name

            if (rendered !== '') {
                trigger.style.removeProperty('anchor-name')
            }
        },

        label() {
            const control = this.control()

            if (!control) {
                return
            }

            control.setAttribute('aria-haspopup', 'menu')
            control.setAttribute('aria-controls', this.$refs.menu.id)
            control.setAttribute('aria-expanded', String(this.isOpen()))
        },

        isOpen() {
            return this.$refs.menu.matches(':popover-open')
        },

        open(focus = 'first') {
            this.label()
            this.anchor()

            if (!this.isOpen()) {
                this.$refs.menu.showPopover()
                this.returnFocus = true
            }

            this.control()?.setAttribute('aria-expanded', 'true')
            this.focusItem(focus)
        },

        close() {
            if (this.isOpen()) {
                this.$refs.menu.hidePopover()
            }

            this.control()?.setAttribute('aria-expanded', 'false')
        },

        toggle(focus = 'first') {
            if (this.isOpen()) {
                this.close()
            } else if (performance.now() - this.closedAt > REOPEN_GUARD_MS) {
                this.open(focus)
            }
        },

        items() {
            return [...this.$refs.menu.querySelectorAll(ITEMS)].filter((item) => item.getAttribute('aria-disabled') !== 'true')
        },

        focusItem(which) {
            const items = this.items()

            ;(which === 'last' ? items.at(-1) : items[0])?.focus()
        },

        navigate(event) {
            const items = this.items()
            const current = items.indexOf(document.activeElement)

            const move = (index) => {
                event.preventDefault()
                items[(index + items.length) % items.length]?.focus()
            }

            switch (event.key) {
                case 'ArrowDown':
                    return move(current + 1)
                case 'ArrowUp':
                    return move(current < 0 ? items.length - 1 : current - 1)
                case 'Home':
                    return move(0)
                case 'End':
                    return move(items.length - 1)
                case 'Escape':
                    this.returnFocus = true

                    return
                case 'Tab':
                    this.returnFocus = false
                    this.close()

                    return
            }

            // Typeahead: a printable letter moves to the next item whose label starts with it.
            if (event.key.length === 1 && !event.ctrlKey && !event.metaKey && !event.altKey) {
                const letter = event.key.toLowerCase()
                const ordered = [...items.slice(current + 1), ...items.slice(0, current + 1)]
                const match = ordered.find((item) => item.textContent.trim().toLowerCase().startsWith(letter))

                if (match) {
                    event.preventDefault()
                    match.focus()
                }
            }
        },

        activate(event) {
            const item = event.target.closest(ITEMS)

            if (!item || item.getAttribute('aria-disabled') === 'true' || item.hasAttribute('data-keep-open')) {
                return
            }

            this.close()
        },

        listen(target, type, handler) {
            target.addEventListener(type, handler)
            this.listeners.push(() => target.removeEventListener(type, handler))
        },

        destroy() {
            this.listeners.forEach((remove) => remove())
        },
    }))
})