深入seajs源码系列二

function Module(uri, deps) {
  this.uri = uri
  this.dependencies = deps || []
  this.exports = null
  this.status = 0

  // Who depends on me
  this._waitings = {}

  // The number of unloaded dependencies
  this._remain = 0
}

var STATUS = Module.STATUS = {
  // 1 - The `module.uri` is being fetched
  FETCHING: 1,
  // 2 - The meta data has been saved to cachedMods
  SAVED: 2,
  // 3 - The `module.dependencies` are being loaded
  LOADING: 3,
  // 4 - The module are ready to execute
  LOADED: 4,
  // 5 - The module is being executed
  EXECUTING: 5,
  // 6 - The `module.exports` is available
  EXECUTED: 6
}

// Define a module
Module.define = function (id, deps, factory) {
  var argsLen = arguments.length

  // define(factory)
  if (argsLen === 1) {
    factory = id
    id = undefined
  }
  else if (argsLen === 2) {
    factory = deps

    // define(deps, factory)
    if (isArray(id)) {
      deps = id
      id = undefined
    }
    // define(id, factory)
    else {
      deps = undefined
    }
  }

  // Parse dependencies according to the module factory code
  // 如果deps为非数组，则序列化工厂函数获取入参。
  if (!isArray(deps) && isFunction(factory)) {
    deps = parseDependencies(factory.toString())
  }

  var meta = {
    id: id,
    uri: Module.resolve(id), // 绝对url
    deps: deps,
    factory: factory
  }

  // Try to derive uri in IE6-9 for anonymous modules
    // 导出匿名模块的uri
  if (!meta.uri && doc.attachEvent) {
    var script = getCurrentScript()

    if (script) {
      meta.uri = script.src
    }

    // NOTE: If the id-deriving methods above is failed, then falls back
    // to use onload event to get the uri
  }

  // Emit `define` event, used in nocache plugin, seajs node version etc
  emit("define", meta)

  meta.uri ? Module.save(meta.uri, meta) :
      // Save information for "saving" work in the script onload event
      anonymousMeta = meta
}

var REQUIRE_RE = /"(?:\\"|[^"])*"|‘(?:\\‘|[^‘])*‘|\/\*[\S\s]*?\*\/|\/(?:\\\/|[^\/\r\n])+\/(?=[^\/])|\/\/.*|\.\s*require|(?:^|[^$])\brequire\s*\(\s*(["‘])(.+?)\1\s*\)/g
var SLASH_RE = /\\\\/g

function parseDependencies(code) {
  var ret = []
  // 此处使用函数序列化（传入的factory）进行字符串匹配，寻找require（“...”）的关键字
  code.replace(SLASH_RE, "")
      .replace(REQUIRE_RE, function(m, m1, m2) {
        if (m2) {
          ret.push(m2)
        }
      })

  return ret
}

function request(url, callback, charset) {
  var isCSS = IS_CSS_RE.test(url)
  var node = doc.createElement(isCSS ? "link" : "script")

  if (charset) {
    var cs = isFunction(charset) ? charset(url) : charset
    if (cs) {
      node.charset = cs
    }
  }

  // 添加 onload 函数。
  addOnload(node, callback, isCSS, url)

  if (isCSS) {
    node.rel = "stylesheet"
    node.href = url
  }
  else {
    node.async = true
    node.src = url
  }

  // For some cache cases in IE 6-8, the script executes IMMEDIATELY after
  // the end of the insert execution, so use `currentlyAddingScript` to
  // hold current node, for deriving url in `define` call
  currentlyAddingScript = node

  // ref: #185 & http://dev.jquery.com/ticket/2709
  baseElement ?
      head.insertBefore(node, baseElement) :
      head.appendChild(node)

  currentlyAddingScript = null
}

function addOnload(node, callback, isCSS, url) {
  var supportOnload = "onload" in node

  // for Old WebKit and Old Firefox
  if (isCSS && (isOldWebKit || !supportOnload)) {
    setTimeout(function() {
      pollCss(node, callback)
    }, 1) // Begin after node insertion
    return
  }

  if (supportOnload) {
    node.onload = onload
    node.onerror = function() {
      emit("error", { uri: url, node: node })
      onload()
    }
  }
  else {
    node.onreadystatechange = function() {
      if (/loaded|complete/.test(node.readyState)) {
        onload()
      }
    }
  }

  function onload() {
    // Ensure only run once and handle memory leak in IE
    node.onload = node.onerror = node.onreadystatechange = null

    // Remove the script to reduce memory leak
    if (!isCSS && !data.debug) {
      head.removeChild(node)
    }

    // Dereference the node
    node = null

    callback()
  }
}
// 针对 旧webkit和不支持onload的CSS节点判断加载完毕的方法
function pollCss(node, callback) {
  var sheet = node.sheet
  var isLoaded

  // for WebKit < 536
  if (isOldWebKit) {
    if (sheet) {
      isLoaded = true
    }
  }
  // for Firefox < 9.0
  else if (sheet) {
    try {
      if (sheet.cssRules) {
        isLoaded = true
      }
    } catch (ex) {
      // The value of `ex.name` is changed from "NS_ERROR_DOM_SECURITY_ERR"
      // to "SecurityError" since Firefox 13.0. But Firefox is less than 9.0
      // in here, So it is ok to just rely on "NS_ERROR_DOM_SECURITY_ERR"
      if (ex.name === "NS_ERROR_DOM_SECURITY_ERR") {
        isLoaded = true
      }
    }
  }

  setTimeout(function() {
    if (isLoaded) {
      // Place callback here to give time for style rendering
      callback()
    }
    else {
      pollCss(node, callback)
    }
  }, 20)
}