JavaScript代码改进

它的书写方式的紧凑性和性能是不相关的。但要以更紧凑、可重用的方式编写它:

function appendScript(url, async) {
    var el = document.createElement('script'),
        root = document.documentElement;
    el.async = async;
    el.src = url;
    // avoid an IE6 bug by using insertBefore (http://bugs.jquery.com/ticket/2709)
    root.insertBefore(el, root.firstChild);
}


appendScript('http://example.com/js/jquery.1.3.2.js', false);
appendScript('http://example.com/js/jquery.alphanumeric.js', false);
appendScript('http://example.com/js/common.js', false);
appendScript(('https:' == document.location.protocol ? '//ssl' : '//www') + '.google-analytics.com/ga.js'), true);

'https:' == document.location.protocol ? 'https://ssl' : 'http://www'

可以变成:

'http' + 'https:'==document.location.protocol ? 's://ssl' : '://www'

这是我能看到的唯一改进,除非您愿意使用非标准javascript,而不是创建元素,而是将实际的html元素添加到字符串中,然后将其附加到documents.innerHTML

var child1 = document.documentElement.firstChild;
child1.appendChild(jq);
child1.appendChild(cm);
child1.appendChild(an);
child1.appendChild(ga);

您可以创建一个addScriptElement()函数来减少重复性。

好吧,这是我的照片。我不确定它现在能省这么多钱,但如果你最终拥有更多的资产 example.com 它会加速事情的发展。

(function(){
    var scripts    = ['jquery.1.3.2', 'jquery.alphanumeric', 'common'],
        head       = document.documentElement.firstChild,
        domain     = 'http://example.com/',
        add_script = function(url, async){
            var script = document.createElement('script');
            script.src = url;
            if(async === true) script.setAttribute('async', 'true');
            head.appendChild(script);
        };

    for(script in scripts) add_script( domain + scripts[script] + '.js' );

    add_script( ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js', true);
})();

这里有一种方法。希望这能使添加或删除脚本变得简单(无论是否需要 async 属性:

({
    DOMAIN : 'http://example.com/',
    SCRIPTS : [ {file:'jquery.1.3.2.js'},
            {file:'jquery.alphanumeric.js'},
            {file:'common.js'},
            {file: ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'
                , async: 'true'} ],
    init: function() {
        for (var i in this.SCRIPTS) {
            var script = this.SCRIPTS[i];
            var sc = document.createElement('script');
            sc.src = (script.file.match(/^http/gi)) ? sc.src = script.file : sc.src = this.DOMAIN + script.file;
            if (typeof script.async !== 'undefined') {
                sc.setAttribute('async', script.async);
            }
            document.documentElement.firstChild.appendChild(sc);
        }

    }
}).init();

我相信这会被否决为'膨胀',但只是分享我将如何做到这一点:

首先,我将定义这样一个高度可扩展的函数:

function addElements(objlist) {
    // One or many
    objlist = [].concat(objlist);

    while(objlist.length > 0) {
        var current = objlist.pop();

        var node = document.createElement(current.element || 'div');
        for(attr in current.attributes)
            node.setAttribute(attr, current.attributes[attr]);

        if(current.parent)
            current.parent.appandChild(node);
    }
}

然后,使用它:

addElements([
    {
        parent: document.documentElement.firstChild,
        element: 'script',
        attributes: {
            src: 'http://example.com/jquery.1.3.2.js'
        }
    },
    {
        parent: document.documentElement.firstChild,
        element: 'script',
        attributes: {
            src: 'http://example.com/jquery.alphanumeric.js'
        }
    },
    {
        parent: document.documentElement.firstChild, 
        element: 'script',
        attributes: {
            src: 'http://example.com/common.js'
        }
    },
    {
        parent: document.documentElement.firstChild, 
        element: 'script',
        attributes: {
            src: ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js',
            async: true
        }
    }
]);

这就是我所说的“幂函数”。它的可读性很强,即使有重复,也能用力量来表达。

您甚至可以自动创建对象:

var elements = [
    'jquery.1.3.2.js',
    'jquery.alphanumeric.js',
    'common.js',
    ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'
];

for(var i=0; i<4; ++i) {
    elements[i] = {
        element: 'script',
        parent: document.documentElement.firstChild,
        attributes: {
            src: 'http://example.com/' + elements[i]
        }
    };
}

elements[3].attributes.async = true;

addElements(elements);