istio.io/archive/v0.5/js/styleswitcher.js

"use strict"

function applyStyleSheet(title) {
    var i, a;
    for (i = 0; (a = document.getElementsByTagName("link")[i]); i++) {
        if (a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title")) {
            a.disabled = true;
            if (a.getAttribute("title") == title) {
                a.disabled = false;
            }
        }
    }

    // set theme-XXX class on the body element
    var b = document.getElementsByTagName("body")[0]
    if (b != undefined) {
        var c = b.getAttribute("class")
        var s = c.split(" ")
        for (i = 0; i < s.length; i++) {
            if (s[i].startsWith("theme-")) {
                s[i] = "theme-" + title
            }
        }
        b.setAttribute("class", s.join(" "))
    }
}

function getPreferredStyleSheet() {
    var i, a;
    for (i = 0; (a = document.getElementsByTagName("link")[i]); i++) {
        if (a.getAttribute("rel").indexOf("style") != -1
            && a.getAttribute("rel").indexOf("alt") == -1
            && a.getAttribute("title")
        ) {
            return a.getAttribute("title");
        }
    }
    return null;
}

function createCookie(name, value, days) {
    if (days) {
        var date = new Date();
        date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
        var expires = "; expires=" + date.toGMTString();
    }
    else {
        expires = "";
    }
    document.cookie = name + "=" + value + expires + "; path=/";
}

function readCookie(name) {
    var nameEQ = name + "=";
    var ca = document.cookie.split(';');
    for (var i = 0; i < ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0) == ' ') {
            c = c.substring(1, c.length);
        }

        if (c.indexOf(nameEQ) == 0) {
            return c.substring(nameEQ.length, c.length);
        }
    }
    return undefined;
}

function setActiveStyleSheet(title) {
    applyStyleSheet(title)
    createCookie("style", title);
}

function loadActiveStyleSheet() {
    var cookie = readCookie("style");
    if (cookie == undefined) {
        applyStyleSheet(getPreferredStyleSheet());
    } else {
        applyStyleSheet(cookie);
    }
}

window.onload = function (e) {
    loadActiveStyleSheet()
}

loadActiveStyleSheet()