assets/js/theme.js


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/* Toggle Dark/Light Mode */
function initThemeToggle() {
    const rootHtml = document.documentElement;
    const toggleThemeBtn = document.getElementById("theme-toggle");

    // The dataset of toggleThemeBtn comes with translated label & title texts for site's language
    function getThemeTexts(theme) {
        const isDarkMode = theme === "dark";
                
        return {
            label: isDarkMode
                ? toggleThemeBtn.dataset.labelLight
                : toggleThemeBtn.dataset.labelDark,
            title: isDarkMode
                ? toggleThemeBtn.dataset.titleLight
                : toggleThemeBtn.dataset.titleDark,
        };
    }

    // Apply correct aria-label and title to the theme toggle button
    function setLabelAndTitle(labelText, titleText) {
        toggleThemeBtn.setAttribute("aria-label", labelText);
        toggleThemeBtn.setAttribute("title", titleText);
    }

    // Apply different theme description to button & root, the display is handled by CSS
    function setTheme(theme) {
        const { label: newLabel, title: newTitle } = getThemeTexts(theme);

        setLabelAndTitle(newLabel, newTitle);
        rootHtml.setAttribute("data-theme", theme);
    }

    // Initial data-theme attribute is set by inline script in <head> on first page load
    const initialTheme = rootHtml.getAttribute("data-theme") ?? "light";
    const { label: initialLabel, title: initialTitle } = getThemeTexts(initialTheme);

    setLabelAndTitle(initialLabel, initialTitle);

    // Change theme on click and save user's choice
    toggleThemeBtn.addEventListener("click", () => {
        const newTheme = rootHtml.getAttribute("data-theme") === "dark" ? "light" : "dark";
        setTheme(newTheme);
        localStorage.setItem("theme", newTheme);
     });
}

export default initThemeToggle;