JS阅读

我读了一下代码，觉得还可以，留个印。

/*
* EnhanceJS version 1.0a - Test-Driven Progressive Enhancement
* Copyright (c) 2010 Filament Group, Inc, authors.txt
* Licensed under MIT (license.txt)
*/
(function(win, doc) {
var settings, body, windowLoaded, head;

if(doc.getElementsByTagName){ head = doc.getElementsByTagName('head')[0] || doc.documentElement; }
else{ head = doc.documentElement; }

enhance = function(options) {
    options  = options || {};
    settings = {};
   
    // mixin settings
    for (var name in enhance.defaultSettings) {
        var option = options[name];
        settings[name] = option !== undefined ? option : enhance.defaultSettings[name];
    }
   
    // mixin additional tests
    for (var test in options.addTests) {
        settings.tests[test] = options.addTests[test];
    }
   
    runTests();
   
    applyDocReadyHack();
   
    windowLoad(function() {
        windowLoaded = true;
    });
};

enhance.defaultTests = {
    getById: function() {
        return !!doc.getElementById;
    },
    getByTagName: function() {
        return !!doc.getElementsByTagName;
    },
    createEl: function() {
        return !!doc.createElement;
    },
    boxmodel: function() {
        var newDiv = doc.createElement('div');
        newDiv.style.cssText = 'width: 1px; padding: 1px;';
        body.appendChild(newDiv);
        var divWidth = newDiv.offsetWidth;
        body.removeChild(newDiv);
        return divWidth === 3;
    },
    position: function() {
        var newDiv = doc.createElement('div');
        newDiv.style.cssText = 'position: absolute; left: 10px;';
        body.appendChild(newDiv);
        var divLeft = newDiv.offsetLeft;
        body.removeChild(newDiv);
        return divLeft === 10;
    },
    floatClear: function() {
        var pass = false,
            newDiv = doc.createElement('div'),
            style = 'style="width: 5px; height: 5px; float: left;"';
        newDiv.innerHTML = '<div ' + style + '></div><div ' + style + '></div>';
        body.appendChild(newDiv);
        var childNodes = newDiv.childNodes,
            topA = childNodes[0].offsetTop,
            divB = childNodes[1],
            topB = divB.offsetTop;
        if (topA === topB) {
            divB.style.clear = 'left';
            topB = divB.offsetTop;
            if (topA !== topB) {
                pass = true;
            }
        }
        body.removeChild(newDiv);
        return pass;
    },
    overflow: function() {
        var newDiv = doc.createElement('div');
        newDiv.innerHTML = '<div style="height: 10px; overflow: hidden;"></div>';
        body.appendChild(newDiv);
        var divHeight = newDiv.offsetHeight;
        body.removeChild(newDiv);
        return divHeight === 10;
    },
    ajax: function() {
        //factory test borrowed from quirksmode.org
        var xmlhttp = false, index = -1, factory,
            XMLHttpFactories = [
                function() { return new XMLHttpRequest() },
                function() { return new ActiveXObject("Msxml2.XMLHTTP") },
                function() { return new ActiveXObject("Msxml3.XMLHTTP") },
                function() { return new ActiveXObject("Microsoft.XMLHTTP") }
            ];
        while ((factory = XMLHttpFactories[++index])) {
            try { xmlhttp = factory(); }
            catch (e) { continue; }
            break;
        }
        return !!xmlhttp;
    },
    resize: function() {
        return win.onresize != false;
    },
    print: function() {
        return !!win.print;
    }
};

enhance.defaultSettings = {
    testName: 'enhanced',
    loadScripts: [],
    loadStyles: [],
    queueLoading: true,
    appendToggleLink: true,
    forcePassText: 'View high-bandwidth version',
    forceFailText: 'View low-bandwidth version',
    tests: enhance.defaultTests,
    addTests: {},
    alertOnFailure: false,
    onPass: function(){},
    onFail: function(){},
    onLoadError: addIncompleteClass
};

function cookiesSupported(){
var testCookie = 'enhancejs-cookietest';
createCookie(testCookie, 'enabled');
var result = readCookie(testCookie);
eraseCookie(testCookie);
return result === 'enabled';
}
enhance.cookiesSupported = cookiesSupported();

function forceFail() {
    createCookie(settings.testName, 'fail');
    win.location.reload();
}
if(enhance.cookiesSupported){ enhance.forceFail = forceFail; }


function forcePass() {
    createCookie(settings.testName, 'pass');
    win.location.reload();
}
if(enhance.cookiesSupported){ enhance.forcePass = forcePass; }

function reTest() {
    eraseCookie(settings.testName);
    win.location.reload();
}
if(enhance.cookiesSupported){ enhance.reTest = reTest; }

function runTests() {
    var result = readCookie(settings.testName);
       
    //check for cookies from a previous test
    if (result) {
        if (result === 'pass') {
            enhancePage();
            settings.onPass();
        } else {
            settings.onFail();
        }
       
        // append toggle link
        if (settings.appendToggleLink) {
            windowLoad(function() {
                appendToggleLinks(result);
            });
        }
    }
    //no cookies - run tests
    else {
        bodyOnReady(function() {
            var pass = true;
            for (var name in settings.tests) {
                pass = settings.tests[name]();
                if (!pass) {
                    if (settings.alertOnFailure) {
                        alert(name + ' failed');
                    }
                    break;
                }
            }
           
            result = pass ? 'pass' : 'fail';
            createCookie(settings.testName, result);
            if (pass) {
                enhancePage();
                settings.onPass();
            } else {
                settings.onFail();
            }
           
            // append toggle link
            if (settings.appendToggleLink) {
                windowLoad(function() {
                    appendToggleLinks(result);
                });
            }
        });
    }
}

function bodyOnReady(callback) {
    var checkBody = setInterval(bodyReady, 1);
    function bodyReady() {
        if (doc.body) {
            body = doc.body;
            clearInterval(checkBody);
            callback();
        }
    }
}

function windowLoad(callback) {
    if (windowLoaded) {
        callback();
    } else {
        var oldonload = win.onload
        win.onload = function() {
            if (oldonload) { oldonload(); }
            callback();
        }
    }
}

function appendToggleLinks(result) {
    if (!settings.appendToggleLink || !enhance.cookiesSupported) { return; }
       
    if (result) {
        var a = doc.createElement('a');
        a.href = "#";
        a.className = settings.testName + '_toggleResult';
        a.innerHTML = result === 'pass' ? settings.forceFailText : settings.forcePassText;
        a.onclick   = result === 'pass' ? enhance.forceFail : enhance.forcePass;
        doc.getElementsByTagName('body')[0].appendChild(a);
    }
}

function enhancePage() {
    if (doc.documentElement.className.indexOf(settings.testName) === -1) {
        doc.documentElement.className += ' ' + settings.testName;
    }
   
    if (settings.loadStyles.length) {
        appendStyles();
    }
    if (settings.loadScripts.length) {
        settings.queueLoading ? appendScriptsSync() : appendScriptsAsync();
    }
}

function addIncompleteClass (){
var errorClass = settings.testName + '-incomplete';
if (doc.documentElement.className.indexOf(errorClass) === -1) {
        doc.documentElement.className += ' ' + errorClass;
    }
}

function appendStyles() {
    var index = -1,
        item;
   
    while ((item = settings.loadStyles[++index])) {
        var link  = doc.createElement('link');
       
        link.type = 'text/css';
        link.rel  = 'stylesheet';
        link.onerror = settings.onLoadError;
       
        if (typeof item === 'string') {
            link.href = item;
            head.appendChild(link);
        }
        else {
            for (var attr in item) {
                if (attr !== 'iecondition') {
                    link.setAttribute(attr, item[attr]);
                }   
            }
            if (item['iecondition'] && isIE()) {
                if (isIE(item['iecondition'])) {
                    head.appendChild(link);
                }
            }
            else if (!item['iecondition']) {
                head.appendChild(link);
            }
        }
    }
}

function isIE(version) {
var isIE = (/MSIE (\d+)\.\d+;/).test(navigator.userAgent);
var ieVersion = new Number(RegExp.$1);
if(isIE && version){
if (version === 'all' || version == ieVersion) { return true; }
}
else{ return isIE; }
}

function appendScriptsSync() {
    var queue = [].concat(settings.loadScripts);
   
    function next() {
        if (queue.length === 0) {
            return;
        }
       
        var item    = queue.shift();
            script = createScriptTag(item),
            done   = false;
        if(script){
        script.onload = script.onreadystatechange = function() {
            if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {
                done = true;
                next();
                this.onload = this.onreadystatechange = null;
            }
        }
        head.insertBefore(script, head.firstChild);
        }
        else{
        next();
        }
    }
   
    next();
}

function appendScriptsAsync() {
    var index = -1,
        item;
       
    while ((item = settings.loadScripts[++index])) {
    var script = createScriptTag(item);
        if(script){
        head.insertBefore(script, head.firstChild);
        }
    }
}

function createScriptTag(item) {
    var script  = doc.createElement('script');
    script.type = 'text/javascript';
    script.onerror = settings.onLoadError;
   
    if (typeof item === 'string') {
        script.src  = item;
        return script;
    }
    else {
        for (var attr in item) {
            if (attr !== 'iecondition') {
                script.setAttribute(attr, item[attr]);
            }   
        }
        if (item['iecondition'] && isIE()) {
            if (isIE(item['iecondition'])) {
                return script;
            }
        }
        else if (!item['iecondition']) {
            return script;
        }
        else{
        return false;
        }
    }
}

/*cookie functions from quirksmode.org*/
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 var expires = "";
    doc.cookie = name+"="+value+expires+"; path=/";
}

function readCookie(name) {
    var nameEQ = name + "=";
    var ca = doc.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 null;
}

function eraseCookie(name) {
    createCookie(name,"",-1);
}


function applyDocReadyHack() {
    // verify that document.readyState is undefined
    // verify that document.addEventListener is there
    // these two conditions are basically telling us
    // we are using Firefox < 3.6
    if (doc.readyState == null && doc.addEventListener){
        // on DOMContentLoaded event, supported since ages
        doc.addEventListener("DOMContentLoaded", function DOMContentLoaded(){
            // remove the listener itself
            doc.removeEventListener("DOMContentLoaded", DOMContentLoaded, false);
            // assign readyState as complete
            doc.readyState = "complete";
        }, false);
        // set readyState = loading or interactive
        // it does not really matter for this purpose
        doc.readyState = "loading";
}
}


})(window, document);