bookwyrm/bookwyrm/static/js/vendor/tabs.js

/* exported TabGroup */

/*
* The content below is licensed according to the W3C Software License at
* https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document
* Heavily modified to web component by Zach Leatherman
* Modified back to vanilla JavaScript with support for Bulma markup and nested tabs by Ned Zimmerman
*/
class TabGroup {
    constructor(container) {
        this.container = container;

        this.tablist = this.container.querySelector('[role="tablist"]');
        this.buttons = this.tablist.querySelectorAll('[role="tab"]');
        this.panels = this.container.querySelectorAll(':scope > [role="tabpanel"]');
        this.delay = this.determineDelay();

        if(!this.tablist || !this.buttons.length || !this.panels.length) {
            return;
        }

        this.keys = this.keys();
        this.direction = this.direction();
        this.initButtons();
        this.initPanels();
    }

    keys() {
        return {
            end: 35,
            home: 36,
            left: 37,
            up: 38,
            right: 39,
            down: 40
        };
    }

    // Add or substract depending on key pressed
    direction() {
        return {
            37: -1,
            38: -1,
            39: 1,
            40: 1
        };
    }

    initButtons() {
        let count = 0;
        for(let button of this.buttons) {
            let isSelected = button.getAttribute("aria-selected") === "true";
            button.setAttribute("tabindex", isSelected ? "0" : "-1");

            button.addEventListener('click', this.clickEventListener.bind(this));
            button.addEventListener('keydown', this.keydownEventListener.bind(this));
            button.addEventListener('keyup', this.keyupEventListener.bind(this));

            button.index = count++;
        }
    }

    initPanels() {
        let selectedPanelId = this.tablist
            .querySelector('[role="tab"][aria-selected="true"]')
            .getAttribute("aria-controls");
        for(let panel of this.panels) {
            if(panel.getAttribute("id") !== selectedPanelId) {
                panel.setAttribute("hidden", "");
            }
            panel.setAttribute("tabindex", "0");
        }
    }

    clickEventListener(event) {
        let button = event.target.closest('a');

        event.preventDefault();

        this.activateTab(button, false);
    }

    // Handle keydown on tabs
    keydownEventListener(event) {
        var key = event.keyCode;

        switch (key) {
            case this.keys.end:
                event.preventDefault();
                // Activate last tab
                this.activateTab(this.buttons[this.buttons.length - 1]);
                break;
            case this.keys.home:
                event.preventDefault();
                // Activate first tab
                this.activateTab(this.buttons[0]);
                break;

            // Up and down are in keydown
            // because we need to prevent page scroll >:)
            case this.keys.up:
            case this.keys.down:
                this.determineOrientation(event);
                break;
        }
    }

    // Handle keyup on tabs
    keyupEventListener(event) {
        var key = event.keyCode;

        switch (key) {
            case this.keys.left:
            case this.keys.right:
                this.determineOrientation(event);
                break;
        }
    }

    // When a tablist’s aria-orientation is set to vertical,
    // only up and down arrow should function.
    // In all other cases only left and right arrow function.
    determineOrientation(event) {
        var key = event.keyCode;
        var vertical = this.tablist.getAttribute('aria-orientation') == 'vertical';
        var proceed = false;

        if (vertical) {
            if (key === this.keys.up || key === this.keys.down) {
                event.preventDefault();
                proceed = true;
            }
        }
        else {
            if (key === this.keys.left || key === this.keys.right) {
                proceed = true;
            }
        }

        if (proceed) {
            this.switchTabOnArrowPress(event);
        }
    }

    // Either focus the next, previous, first, or last tab
    // depending on key pressed
    switchTabOnArrowPress(event) {
        var pressed = event.keyCode;

        for (let button of this.buttons) {
            button.addEventListener('focus', this.focusEventHandler.bind(this));
        }

        if (this.direction[pressed]) {
            var target = event.target;
            if (target.index !== undefined) {
                if (this.buttons[target.index + this.direction[pressed]]) {
                    this.buttons[target.index + this.direction[pressed]].focus();
                }
                else if (pressed === this.keys.left || pressed === this.keys.up) {
                    this.focusLastTab();
                }
                else if (pressed === this.keys.right || pressed == this.keys.down) {
                    this.focusFirstTab();
                }
            }
        }
    }

    // Activates any given tab panel
    activateTab (tab, setFocus) {
        if(tab.getAttribute("role") !== "tab") {
            tab = tab.closest('[role="tab"]');
        }

        setFocus = setFocus || true;

        // Deactivate all other tabs
        this.deactivateTabs();

        // Remove tabindex attribute
        tab.removeAttribute('tabindex');

        // Set the tab as selected
        tab.setAttribute('aria-selected', 'true');

        // Give the tab parent an is-active class
        tab.parentNode.classList.add('is-active');

        // Get the value of aria-controls (which is an ID)
        var controls = tab.getAttribute('aria-controls');

        // Remove hidden attribute from tab panel to make it visible
        document.getElementById(controls).removeAttribute('hidden');

        // Set focus when required
        if (setFocus) {
            tab.focus();
        }
    }

    // Deactivate all tabs and tab panels
    deactivateTabs() {
        for (let button of this.buttons) {
            button.parentNode.classList.remove('is-active');
            button.setAttribute('tabindex', '-1');
            button.setAttribute('aria-selected', 'false');
            button.removeEventListener('focus', this.focusEventHandler.bind(this));
        }

        for (let panel of this.panels) {
            panel.setAttribute('hidden', 'hidden');
        }
    }

    focusFirstTab() {
        this.buttons[0].focus();
    }

    focusLastTab() {
        this.buttons[this.buttons.length - 1].focus();
    }

    // Determine whether there should be a delay
    // when user navigates with the arrow keys
    determineDelay() {
        var hasDelay = this.tablist.hasAttribute('data-delay');
        var delay = 0;

        if (hasDelay) {
            var delayValue = this.tablist.getAttribute('data-delay');
            if (delayValue) {
                delay = delayValue;
            }
            else {
                // If no value is specified, default to 300ms
                delay = 300;
            }
        }

        return delay;
    }

    focusEventHandler(event) {
        var target = event.target;

        setTimeout(this.checkTabFocus.bind(this), this.delay, target);
    }

    // Only activate tab on focus if it still has focus after the delay
    checkTabFocus(target) {
        let focused = document.activeElement;

        if (target === focused) {
            this.activateTab(target, false);
        }
    }
}