bookwyrm/bookwyrm/static/js/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.tabs = this.tablist.querySelectorAll('[role="tab"]');
        this.panels = this.container.querySelectorAll(':scope > [role="tabpanel"]');
        this.delay = this.determineDelay();

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

        this.keys = this.keys();
        this.direction = this.direction();
        this.initTabs();
        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,
        };
    }

    initTabs() {
        let count = 0;

        for (let tab of this.tabs) {
            let isSelected = tab.getAttribute("aria-selected") === "true";

            tab.setAttribute("tabindex", isSelected ? "0" : "-1");

            tab.addEventListener("click", this.clickEventListener.bind(this));
            tab.addEventListener("keydown", this.keydownEventListener.bind(this));
            tab.addEventListener("keyup", this.keyupEventListener.bind(this));

            tab.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 tab = event.target.closest('[role="tab"]');

        event.preventDefault();

        this.activateTab(tab, false);
    }

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

        switch (key) {
            case this.keys.end:
                event.preventDefault();

                // Activate last tab
                this.activateTab(this.tabs[this.tabs.length - 1]);
                break;
            case this.keys.home:
                event.preventDefault();

                // Activate first tab
                this.activateTab(this.tabs[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) {
        const 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) {
        const key = event.keyCode;
        const vertical = this.tablist.getAttribute("aria-orientation") == "vertical";
        let 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) {
        const pressed = event.keyCode;

        for (let tab of this.tabs) {
            tab.addEventListener("focus", this.focusEventHandler.bind(this));
        }

        if (this.direction[pressed]) {
            const target = event.target;

            if (target.index !== undefined) {
                if (this.tabs[target.index + this.direction[pressed]]) {
                    this.tabs[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 is-active class
        tab.classList.add("is-active");

        // Get the value of aria-controls (which is an ID)
        const 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 tab of this.tabs) {
            tab.classList.remove("is-active");
            tab.setAttribute("tabindex", "-1");
            tab.setAttribute("aria-selected", "false");
            tab.removeEventListener("focus", this.focusEventHandler.bind(this));
        }

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

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

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

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

        if (hasDelay) {
            const 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) {
        const 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);
        }
    }
}