最近开始学习Zepto源代码，分享出来，共同学习。前端新人，技术欠佳，多多见谅
参考的gitbook地址
感谢作者奉献

zepto的css选择器zepto.qsa

我们都知道，很多时候，我们都用$来获取DOM对象，这跟zepto.qsa有很大的关系。

获取selector[0]
如果为ID getElementById处理
如果为calss getElementsByClassName处理
如果为tagName getElementsByTagName处理
非但选择器 querySelectorAll处理
最后选择才调用querySelectorAll是因为querySelectorAll耗费性能太高
参考静态的nodelist对比动态的nodelist

zepto.qsa = function (element, selector) {
    var found,
        maybeID = selector[0] == '#',
        maybeClass = !maybeID && selector[0] == '.',
        nameOnly = maybeID || maybeClass ? selector.slice(1) : selector, // Ensure that a 1 char tag name still gets checked
        isSimple = simpleSelectorRE.test(nameOnly)
    return (element.getElementById && isSimple && maybeID) ? // Safari DocumentFragment doesn't have getElementById
        ((found = element.getElementById(nameOnly)) ? [found] : []) :
        (element.nodeType !== 1 && element.nodeType !== 9 && element.nodeType !== 11) ? [] :
            slice.call(
                isSimple && !maybeID && element.getElementsByClassName ? // DocumentFragment doesn't have getElementsByClassName/TagName
                    maybeClass ? element.getElementsByClassName(nameOnly) : // If it's simple, it could be a class
                        element.getElementsByTagName(selector) : // Or a tag
                    element.querySelectorAll(selector) // Or it's not simple, and we need to query all
            )
}

zepto.Z 函数
返回new Z函数

zepto.Z = function (dom, selector) {
        return new Z(dom, selector)
}

Z函数 返回数组

function Z(dom, selector) {
        var i, len = dom ? dom.length : 0
        for (i = 0; i < len; i++) this[i] = dom[i]
        this.length = len
        this.selector = selector || ''
}

isZ 判断是否是Z函数

zepto.isZ = function (object) {
        return object instanceof zepto.Z
}

zepto.init 初始化函数

    zepto.init = function (selector, context) {
        var dom
        // If nothing given, return an empty Zepto collection
        if (!selector) return zepto.Z()
        // Optimize for string selectors
        else if (typeof selector == 'string') {
            selector = selector.trim()
            // If it's a html fragment, create nodes from it
            // Note: In both Chrome 21 and Firefox 15, DOM error 12
            // is thrown if the fragment doesn't begin with <
            if (selector[0] == '<' && fragmentRE.test(selector))
                dom = zepto.fragment(selector, RegExp.$1, context), selector = null, console.log(dom)
            // If there's a context, create a collection on that context first, and select
            // nodes from there
            else if (context !== undefined) return $(context).find(selector)
            // If it's a CSS selector, use it to select nodes.
            else dom = zepto.qsa(document, selector), console.log(dom, 123123);

        }
        // If a function is given, call it when the DOM is ready
        else if (isFunction(selector)) return $(document).ready(selector)
        // If a Zepto collection is given, just return it
        else if (zepto.isZ(selector)) return selector
        else {
            // normalize array if an array of nodes is given
            if (isArray(selector)) {
              dom = compact(selector)
              console.log(dom);
            }
            // Wrap DOM nodes.
            else if (isObject(selector))
                dom = [selector], selector = null
            // If it's a html fragment, create nodes from it
            else if (fragmentRE.test(selector))
                dom = zepto.fragment(selector.trim(), RegExp.$1, context), selector = null
            // If there's a context, create a collection on that context first, and select
            // nodes from there
            else if (context !== undefined) return $(context).find(selector)
            // And last but no least, if it's a CSS selector, use it to select nodes.
            else dom = zepto.qsa(document, selector)
        }
        // create a new Zepto collection from the nodes found
        return zepto.Z(dom, selector)
    }