rust-clippy/util/gh-pages/theme.js

function storeValue(settingName, value) {
    try {
        localStorage.setItem(`clippy-lint-list-${settingName}`, value);
    } catch (e) { }
}

function loadValue(settingName) {
    return localStorage.getItem(`clippy-lint-list-${settingName}`);
}

function setTheme(theme, store) {
    let enableHighlight = false;
    let enableNight = false;
    let enableAyu = false;

    switch(theme) {
        case "ayu":
            enableAyu = true;
            break;
        case "coal":
        case "navy":
            enableNight = true;
            break;
        case "rust":
            enableHighlight = true;
            break;
        default:
            enableHighlight = true;
            theme = "light";
            break;
    }

    document.body.className = theme;

    document.getElementById("githubLightHighlight").disabled = enableNight || !enableHighlight;
    document.getElementById("githubDarkHighlight").disabled = !enableNight && !enableAyu;

    document.getElementById("styleHighlight").disabled = !enableHighlight;
    document.getElementById("styleNight").disabled = !enableNight;
    document.getElementById("styleAyu").disabled = !enableAyu;

    if (store) {
        storeValue("theme", theme);
    }
}

(function() {
    // loading the theme after the initial load
    const prefersDark = window.matchMedia("(prefers-color-scheme: dark)");
    const theme = loadValue("theme");
    if (prefersDark.matches && !theme) {
        setTheme("coal", false);
    } else {
        setTheme(theme, false);
    }
})();