zepto源码分析------ajax篇

  $.ajax = function(options) {
    // 覆盖配置
    var settings = $.extend({}, options || {}),
      // 没有找到在哪里
      deferred = $.Deferred && $.Deferred(),
      urlAnchor
    // 完成完整对配置覆盖
    for (key in $.ajaxSettings)
      if (settings[key] === undefined) settings[key] = $.ajaxSettings[key]

    // 这里要涉及到三个函数 ajaxStart>triggerGlobal>triggerAndReturn(触发ajax)
    ajaxStart(settings)

    // 是跨域
    if (!settings.crossDomain) {
      urlAnchor = document.createElement(‘a‘)
      urlAnchor.href = settings.url
      urlAnchor.href = urlAnchor.href
      // 验证是否真的跨域了----确保对参数的修正
      settings.crossDomain = (originAnchor.protocol + ‘//‘ + originAnchor.host) !== (urlAnchor.protocol + ‘//‘ + urlAnchor.host)
    }

    if (!settings.url) settings.url = window.location.toString()
    // 序列化数据
    serializeData(settings)

    var dataType = settings.dataType,
    // 解析地址如果存在回调那么hasplaceholder = true
      hasPlaceholder = /\?.+=\?/.test(settings.url)

    if (hasPlaceholder) dataType = ‘jsonp‘

    if (settings.cache === false || (
        (!options || options.cache !== true) &&
        (‘script‘ == dataType || ‘jsonp‘ == dataType)
      ))
      // 增加一个选择器(不是很明白)
      settings.url = appendQuery(settings.url, ‘_=‘ + Date.now())

    if (‘jsonp‘ == dataType) {
      if (!hasPlaceholder)
        settings.url = appendQuery(settings.url,
          settings.jsonp ? (settings.jsonp + ‘=?‘) : settings.jsonp === false ? ‘‘ : ‘callback=?‘)
      // 如果是跨域则用jsonp跨域
      return $.ajaxJSONP(settings, deferred)
    }

    var mime = settings.accepts[dataType],
      headers = {},
      setHeader = function(name, value) {
        headers[name.toLowerCase()] = [name, value]
      },
      protocol = /^([\w-]+:)\/\//.test(settings.url) ? RegExp.$1 : window.location.protocol,
      xhr = settings.xhr(),
      nativeSetHeader = xhr.setRequestHeader,
      abortTimeout

    if (deferred) deferred.promise(xhr)

    // 如果是跨域请求
    if (!settings.crossDomain) setHeader(‘X-Requested-With‘, ‘XMLHttpRequest‘)
    setHeader(‘Accept‘, mime || ‘*/*‘)
    if (mime = settings.mimeType || mime) {
      if (mime.indexOf(‘,‘) > -1) mime = mime.split(‘,‘, 2)[0]
      xhr.overrideMimeType && xhr.overrideMimeType(mime)
    }
    if (settings.contentType || (settings.contentType !== false && settings.data && settings.type.toUpperCase() != ‘GET‘))
      setHeader(‘Content-Type‘, settings.contentType || ‘application/x-www-form-urlencoded‘)

    if (settings.headers)
      for (name in settings.headers) setHeader(name, settings.headers[name])
    xhr.setRequestHeader = setHeader

    // 监听请求状态
    xhr.onreadystatechange = function() {
      if (xhr.readyState == 4) {
        xhr.onreadystatechange = empty
        clearTimeout(abortTimeout)
        var result, error = false
        if ((xhr.status >= 200 && xhr.status < 300) || xhr.status == 304 || (xhr.status == 0 && protocol == ‘file:‘)) {
          dataType = dataType || mimeToDataType(settings.mimeType || xhr.getResponseHeader(‘content-type‘))
          result = xhr.responseText

          try {
            // http://perfectionkills.com/global-eval-what-are-the-options/
            if (dataType == ‘script‘)(1, eval)(result)
            else if (dataType == ‘xml‘) result = xhr.responseXML
            else if (dataType == ‘json‘) result = blankRE.test(result) ? null : $.parseJSON(result)
          } catch (e) {
            error = e
          }

          if (error) ajaxError(error, ‘parsererror‘, xhr, settings, deferred)
          else ajaxSuccess(result, xhr, settings, deferred)
        } else {
          ajaxError(xhr.statusText || null, xhr.status ? ‘error‘ : ‘abort‘, xhr, settings, deferred)
        }
      }
    }

    if (ajaxBeforeSend(xhr, settings) === false) {
      xhr.abort()
      ajaxError(null, ‘abort‘, xhr, settings, deferred)
      return xhr
    }

    if (settings.xhrFields)
      for (name in settings.xhrFields) xhr[name] = settings.xhrFields[name]

    // 设置异步和同步
    var async = ‘async‘ in settings ? settings.async : true
    xhr.open(settings.type, settings.url, async, settings.username, settings.password)

    for (name in headers) nativeSetHeader.apply(xhr, headers[name])

    if (settings.timeout > 0) abortTimeout = setTimeout(function() {
      xhr.onreadystatechange = empty
      xhr.abort()
      ajaxError(null, ‘timeout‘, xhr, settings, deferred)
    }, settings.timeout)

    // avoid sending empty string (#319)
    xhr.send(settings.data ? settings.data : null)
    return xhr
  }

 $.ajaxJSONP = function(options, deferred) {
    if (!(‘type‘ in options)) return $.ajax(options)

    var _callbackName = options.jsonpCallback,
      callbackName = ($.isFunction(_callbackName) ?
        _callbackName() : _callbackName) || (‘jsonp‘ + (++jsonpID)),
      script = document.createElement(‘script‘),
      originalCallback = window[callbackName],
      responseData,
      abort = function(errorType) {
        $(script).triggerHandler(‘error‘, errorType || ‘abort‘)
      },
      xhr = {
        abort: abort
      },
      abortTimeout

    if (deferred) deferred.promise(xhr)

    $(script).on(‘load error‘, function(e, errorType) {
      clearTimeout(abortTimeout)
      $(script).off().remove()

      if (e.type == ‘error‘ || !responseData) {
        ajaxError(null, errorType || ‘error‘, xhr, options, deferred)
      } else {
        ajaxSuccess(responseData[0], xhr, options, deferred)
      }

      window[callbackName] = originalCallback
      if (responseData && $.isFunction(originalCallback))
        originalCallback(responseData[0])

      originalCallback = responseData = undefined
    })

    if (ajaxBeforeSend(xhr, options) === false) {
      abort(‘abort‘)
      return xhr
    }

    window[callbackName] = function() {
      responseData = arguments
    }

    script.src = options.url.replace(/\?(.+)=\?/, ‘?$1=‘ + callbackName)
    document.head.appendChild(script)

    if (options.timeout > 0) abortTimeout = setTimeout(function() {
      abort(‘timeout‘)
    }, options.timeout)

    return xhr
  }