rust/src/librustdoc/html/static/storage.js

/*!
 * Copyright 2018 The Rust Project Developers. See the COPYRIGHT
 * file at the top-level directory of this distribution and at
 * http://rust-lang.org/COPYRIGHT.
 *
 * Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 * http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 * <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 * option. This file may not be copied, modified, or distributed
 * except according to those terms.
 */

var currentTheme = document.getElementById("themeStyle");
var mainTheme = document.getElementById("mainThemeStyle");

var savedHref = [];

function hasClass(elem, className) {
    if (elem && className && elem.className) {
        var elemClass = elem.className;
        var start = elemClass.indexOf(className);
        if (start === -1) {
            return false;
        } else if (elemClass.length === className.length) {
            return true;
        } else {
            if (start > 0 && elemClass[start - 1] !== ' ') {
                return false;
            }
            var end = start + className.length;
            return !(end < elemClass.length && elemClass[end] !== ' ');
        }
    }
    return false;
}

function addClass(elem, className) {
    if (elem && className && !hasClass(elem, className)) {
        if (elem.className && elem.className.length > 0) {
            elem.className += ' ' + className;
        } else {
            elem.className = className;
        }
    }
}

function removeClass(elem, className) {
    if (elem && className && elem.className) {
        elem.className = (" " + elem.className + " ").replace(" " + className + " ", " ")
                                                     .trim();
    }
}

function isHidden(elem) {
    return (elem.offsetParent === null)
}

function onEach(arr, func, reversed) {
    if (arr && arr.length > 0 && func) {
        if (reversed !== true) {
            for (var i = 0; i < arr.length; ++i) {
                if (func(arr[i]) === true) {
                    return true;
                }
            }
        } else {
            for (var i = arr.length - 1; i >= 0; --i) {
                if (func(arr[i]) === true) {
                    return true;
                }
            }
        }
    }
    return false;
}

function usableLocalStorage() {
    // Check if the browser supports localStorage at all:
    if (typeof(Storage) === "undefined") {
        return false;
    }
    // Check if we can access it; this access will fail if the browser
    // preferences deny access to localStorage, e.g., to prevent storage of
    // "cookies" (or cookie-likes, as is the case here).
    try {
        window.localStorage;
    } catch(err) {
        // Storage is supported, but browser preferences deny access to it.
        return false;
    }

    return true;
}

function updateLocalStorage(name, value) {
    if (usableLocalStorage()) {
        localStorage[name] = value;
    } else {
        // No Web Storage support so we do nothing
    }
}

function getCurrentValue(name) {
    if (usableLocalStorage() && localStorage[name] !== undefined) {
        return localStorage[name];
    }
    return null;
}

function switchTheme(styleElem, mainStyleElem, newTheme) {
    var fullBasicCss = "rustdoc" + resourcesSuffix + ".css";
    var fullNewTheme = newTheme + resourcesSuffix + ".css";
    var newHref = mainStyleElem.href.replace(fullBasicCss, fullNewTheme);

    if (styleElem.href === newHref) {
        return;
    }

    var found = false;
    if (savedHref.length === 0) {
        onEach(document.getElementsByTagName("link"), function(el) {
            savedHref.push(el.href);
        });
    }
    onEach(savedHref, function(el) {
        if (el === newHref) {
            found = true;
            return true;
        }
    });
    if (found === true) {
        styleElem.href = newHref;
        updateLocalStorage('rustdoc-theme', newTheme);
    }
}

switchTheme(currentTheme, mainTheme, getCurrentValue('rustdoc-theme') || 'light');