Sea.Js的运行原理

// Use function is equal to load a anonymous module
Module.use = function (ids, callback, uri) {
    var mod = Module.get(uri, isArray(ids) ? ids: [ids])

    mod.callback = function () {
        var exports = []
        var uris = mod.resolve()

        for (var i = 0, len = uris.length; i < len; i++) {
            exports[i] = cachedMods[uris[i]].exec()
        }

        if (callback) {
            callback.apply(global, exports)
        }

        delete mod.callback
    }

    mod.load()
}

// Load module.dependencies and fire onload when all done
Module.prototype.load = function () {
    var mod = this

    // If the module is being loaded, just wait it onload call
    if (mod.status >= STATUS.LOADING) {
        return
    }

    mod.status = STATUS.LOADING

    // Emit `load` event for plugins such as combo plugin
    var uris = mod.resolve()
    emit("load", uris)

    var len = mod._remain = uris.length
    var m

    // Initialize modules and register waitings
    for (var i = 0; i < len; i++) {
        m = Module.get(uris[i])

        if (m.status < STATUS.LOADED) {
            // Maybe duplicate
            m._waitings[mod.uri] = (m._waitings[mod.uri] || 0) + 1
        }
        else {
            mod._remain--
        }
    }

    if (mod._remain === 0) {
        mod.onload()
        return
    }

    // Begin parallel loading
    var requestCache = {}

    for (i = 0; i < len; i++) {
        m = cachedMods[uris[i]]

        if (m.status < STATUS.FETCHING) {
            m.fetch(requestCache)
        }
        else if (m.status === STATUS.SAVED) {
            m.load()
        }
    }

    // Send all requests at last to avoid cache bug in IE6-9. Issues#808
    for (var requestUri in requestCache) {
        if (requestCache.hasOwnProperty(requestUri)) {
            requestCache[requestUri]()
        }
    }
}

// Call this method when module is loaded
Module.prototype.onload = function () {
    var mod = this
    mod.status = STATUS.LOADED

    if (mod.callback) {
        mod.callback()
    }

    // Notify waiting modules to fire onload
    var waitings = mod._waitings
    var uri, m

    for (uri in waitings) {
        if (waitings.hasOwnProperty(uri)) {
            m = cachedMods[uri]
            m._remain -= waitings[uri]
            if (m._remain === 0) {
                m.onload()
            }
        }
    }

    // Reduce memory taken
    delete mod._waitings
    delete mod._remain
}

mod.callback = function () {
    var exports = []
    var uris = mod.resolve()

    for (var i = 0, len = uris.length; i < len; i++) {
        exports[i] = cachedMods[uris[i]].exec()
    }

    if (callback) {
        callback.apply(global, exports)
    }

    delete mod.callback
}

// Execute a module
Module.prototype.exec = function () {
    var mod = this

    // When module is executed, DO NOT execute it again. When module
    // is being executed, just return `module.exports` too, for avoiding
    // circularly calling
    if (mod.status >= STATUS.EXECUTING) {
        return mod.exports
    }

    mod.status = STATUS.EXECUTING

    // Create require
    var uri = mod.uri

    function require(id) {
        return Module.get(require.resolve(id)).exec()
    }

    require.resolve = function (id) {
        return Module.resolve(id, uri)
    }

    require.async = function (ids, callback) {
        Module.use(ids, callback, uri + "_async_" + cid())
        return require
    }

    // Exec factory
    var factory = mod.factory

    var exports = isFunction(factory) ? factory(require, mod.exports = {},
    mod) : factory

    if (exports === undefined) {
        exports = mod.exports
    }

    // Emit `error` event
    if (exports === null && ! IS_CSS_RE.test(uri)) {
        emit("error", mod)
    }

    // Reduce memory leak
    delete mod.factory

    mod.exports = exports
    mod.status = STATUS.EXECUTED

    // Emit `exec` event
    emit("exec", mod)

    return exports
}

/**
 * util-deps.js - The parser for dependencies
 * ref: tests/research/parse-dependencies/test.html
 */

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

function parseDependencies(code) {
  var ret = []

  code.replace(SLASH_RE, "")
      .replace(REQUIRE_RE, function(m, m1, m2) {
        if (m2) {
          ret.push(m2)
        }
      })

  return ret
}