.31-浅析webpack源码之doResolve事件流(3)

2018-06-24 01:24:36来源：未知阅读 ()

　　放个流程图：

　　这里也放一下request对象内容，这节完事后如下(把vue-cli的package.json也复制过来了)：

/*
    { 
        context: { issuer: '', compiler: undefined },
        path: 'd:\\workspace\\doc',
        request: './input.js',
        query: '',
        module: false,
        directory: false,
        file: false,
        descriptionFilePath: 'd:\\workspace\\doc\\package.json',
        descriptionFileData: *package.json内容*,
        descriptionFileRoot: 'd:\\workspace\\doc',
        relativePath: '.',
        __innerRequest_request: './input.js',
        __innerRequest_relativePath: '.',
        __innerRequest: './input.js' 
    }
*/

　　上一节看到这：

// 调用的是callback()
function innerCallback(err, result) {
    if (arguments.length > 0) {
        if (err) return callback(err);
        if (result) return callback(null, result);
        return callback();
    }
    runAfter();
}

　　这里接下来会调用runAfter方法，之前有讲解过这个，简单讲就是触发after-type的事件流，这里的type为parsed-resolve，即触发after-parsed-resolve事件流。

　　来源如下：

plugins.push(new NextPlugin("after-parsed-resolve", "described-resolve"));

　　这个插件就非常简单了：

NextPlugin.prototype.apply = function(resolver) {
    var target = this.target;
    resolver.plugin(this.source, function(request, callback) {
        resolver.doResolve(target, request, null, callback);
    });
};

　　直接调用doResolve方法触发下一个target的事件流，比起有描述文件的情况，这里的区别就是request少了几个参数，触发下一个事件流时没有message。

　　刚发现事件流的名字代表着某阶段，此时代表描述文件解析完毕。

　　接下来的事件流来源于以下几个插件：

// described-resolve
alias.forEach(function(item) {
    plugins.push(new AliasPlugin("described-resolve", item, "resolve"));
});
plugins.push(new ConcordModulesPlugin("described-resolve", {}, "resolve"));
aliasFields.forEach(function(item) {
    plugins.push(new AliasFieldPlugin("described-resolve", item, "resolve"));
});
plugins.push(new ModuleKindPlugin("after-described-resolve", "raw-module"));
plugins.push(new JoinRequestPlugin("after-described-resolve", "relative"));

AliasPlugin　　

　　先从第一个开始看，alias参数引用vue-cli的代码，这里的alias在上面的第二部分进行了转换(具体可参考28节)。

　　数组的元素作为参数传入了AliasPlugin插件中，源码如下：

/*
源配置
    alias: {
        'vue$': 'vue/dist/vue.esm.js',
        '@': '../src'
    }
转换后为
    alias:[
        {
            name: 'vue',
            onlyModule: true,
            alias: 'vue/dist/vue.esm.js'
        },
        {
            name: '@',
            onlyModule: false,
            alias: '../src'           
        }
    ]
*/
AliasPlugin.prototype.apply = function(resolver) {
    var target = this.target;
    var name = this.name;
    var alias = this.alias;
    var onlyModule = this.onlyModule;
    resolver.plugin(this.source, function(request, callback) {
        var innerRequest = request.request;
        if (!innerRequest) return callback();
        // 两个元素传进来并不满足if条件 跳过
        // startsWith可参考ES6的新方法http://es6.ruanyifeng.com/#docs/string#includes-startsWith-endsWith
        if (innerRequest === name || (!onlyModule && startsWith(innerRequest, name + "/"))) {
            if (innerRequest !== alias && !startsWith(innerRequest, alias + "/")) {
                var newRequestStr = alias + innerRequest.substr(name.length);
                var obj = Object.assign({}, request, {
                    request: newRequestStr
                });
                return resolver.doResolve(target, obj, "aliased with mapping '" + name + "': '" + alias + "' to '" + newRequestStr + "'", createInnerCallback(function(err, result) {
                    if (arguments.length > 0) return callback(err, result);

                    // don't allow other aliasing or raw request
                    callback(null, null);
                }, callback));
            }
        }
        return callback();
    });
};

　　不太懂这里的处理是干什么，反正两个元素传进来都没有满足if条件，跳过。

ConcordModulesPlugin

　　described-resolve事件流还没有完，所以callback执行后只是记数，下一个插件源码如下：

ConcordModulesPlugin.prototype.apply = function(resolver) {
    var target = this.target;
    resolver.plugin(this.source, function(request, callback) {
        // 获取的还是'./input.js'
        var innerRequest = getInnerRequest(resolver, request);
        if (!innerRequest) return callback();
        // request.descriptionFileData就是配置文件package.json中的内容
        var concordField = DescriptionFileUtils.getField(request.descriptionFileData, "concord");
        // 找不到该属性直接返回
        if (!concordField) return callback();
        // 下面的都不用跑了
        var data = concord.matchModule(request.context, concordField, innerRequest);
        if (data === innerRequest) return callback();
        if (data === undefined) return callback();
        if (data === false) {
            var ignoreObj = Object.assign({}, request, {
                path: false

            });
            return callback(null, ignoreObj);
        }
        var obj = Object.assign({}, request, {
            path: request.descriptionFileRoot,
            request: data
        });
        resolver.doResolve(target, obj, "aliased from description file " + request.descriptionFilePath + " with mapping '" + innerRequest + "' to '" + data + "'", createInnerCallback(function(err, result) {
            if (arguments.length > 0) return callback(err, result);

            // Don't allow other aliasing or raw request
            callback(null, null);
        }, callback));
    });
};

　　这里有两个工具方法：getInnerRequest、getFiled，第一个获取request的inner属性，代码如下：

module.exports = function getInnerRequest(resolver, request) {
    // 第一次进来是没有这些属性的
    if (typeof request.__innerRequest === "string" &&
        request.__innerRequest_request === request.request &&
        request.__innerRequest_relativePath === request.relativePath)
        return request.__innerRequest;
    var innerRequest;
    // './input.js'
    if (request.request) {
        innerRequest = request.request;
        // 尝试获取relativePath属性进行拼接
        if (/^\.\.?\//.test(innerRequest) && request.relativePath) {
            innerRequest = resolver.join(request.relativePath, innerRequest);
        }
    } else {
        innerRequest = request.relativePath;
    }
    // 属性添加
    request.__innerRequest_request = request.request;
    request.__innerRequest_relativePath = request.relativePath;
    return request.__innerRequest = innerRequest;
};

　　总的来说就是尝试获取__innerRequest属性，但是初次进来是没有的，所以会在后面进行添加，最后返回的仍然是'./input.js'。

　　第二个方法就比较简单了，只是从之前读取的package.json对象查询对应的字段，代码如下：

// content为package.json配置对象
function getField(content, field) {
    if (!content) return undefined;
    // 数组及单key模式
    if (Array.isArray(field)) {
        var current = content;
        for (var j = 0; j < field.length; j++) {
            if (current === null || typeof current !== "object") {
                current = null;
                break;
            }
            current = current[field[j]];
        }
        if (typeof current === "object") {
            return current;
        }
    } else {
        if (typeof content[field] === "object") {
            return content[field];
        }
    }
}

　　代码非常简单，这里就不讲了。

　　常规情况下，没人会去设置concord属性吧，在vue-cli我也没看到，这里先跳过。

AliasFieldPlugin

　　接下来是这个不知道干啥的插件，处理的是resolve.aliasFields参数，默认参数及插件源码如下：

// "aliasFields": ["browser"],
AliasFieldPlugin.prototype.apply = function(resolver) {
    var target = this.target;
    var field = this.field;
    resolver.plugin(this.source, function(request, callback) {
        if (!request.descriptionFileData) return callback();
        // 一样的
        var innerRequest = getInnerRequest(resolver, request);
        if (!innerRequest) return callback();
        // filed => browser
        var fieldData = DescriptionFileUtils.getField(request.descriptionFileData, field);
        if (typeof fieldData !== "object") {
            if (callback.log) callback.log("Field '" + field + "' doesn't contain a valid alias configuration");
            return callback();
        }
        var data1 = fieldData[innerRequest];
        var data2 = fieldData[innerRequest.replace(/^\.\//, "")];
        var data = typeof data1 !== "undefined" ? data1 : data2;
        if (data === innerRequest) return callback();
        if (data === undefined) return callback();
        if (data === false) {
            var ignoreObj = Object.assign({}, request, {
                path: false
            });
            return callback(null, ignoreObj);
        }
        var obj = Object.assign({}, request, {
            path: request.descriptionFileRoot,
            request: data
        });
        resolver.doResolve(target, obj, "aliased from description file " + request.descriptionFilePath + " with mapping '" + innerRequest + "' to '" + data + "'", createInnerCallback(function(err, result) {
            if (arguments.length > 0) return callback(err, result);

            // Don't allow other aliasing or raw request
            callback(null, null);
        }, callback));
    });
};

　　开头跟之前那个是一样的，也是调用getField从package.json中获取对应的配置，但是这个默认的browser我在vue-cli也找不到，暂时跳过。

　　正常处理完described-resolve事件流，继续执行runafter触发after-described-resolve事件流，来源如下：

plugins.push(new ModuleKindPlugin("after-described-resolve", "raw-module"));
plugins.push(new JoinRequestPlugin("after-described-resolve", "relative"));

ModuleKindPlugin

ModuleKindPlugin.prototype.apply = function(resolver) {
    var target = this.target;
    resolver.plugin(this.source, function(request, callback) {
        // 判断module属性
        if (!request.module) return callback();
        var obj = Object.assign({}, request);
        // 删除module属性
        delete obj.module;
        // 直接触发下一个事件流
        resolver.doResolve(target, obj, "resolve as module", createInnerCallback(function(err, result) {
            if (arguments.length > 0) return callback(err, result);

            // Don't allow other alternatives
            callback(null, null);
        }, callback));
    });
};

　　这里的处理十分简单，判断request对象是否是module，是则直接触发下一个事件流。

　　而在第一次时进来的是入口文件，module属性为false，所以这里会跳过，后面处理module再回来讲。

JoinRequestPlugin

JoinRequestPlugin.prototype.apply = function(resolver) {
    var target = this.target;
    resolver.plugin(this.source, function(request, callback) {
        var obj = Object.assign({}, request, {
            // request.path => d:\\workspace\\doc
            // request.request => ./input.js
            // 在join方法中会被拼接成d:\workspace\doc\.\input.js
            // 最后格式化返回d:\workspace\doc\input.js
            path: resolver.join(request.path, request.request),
            // undefined
            relativePath: request.relativePath && resolver.join(request.relativePath, request.request),
            request: undefined
        });
        resolver.doResolve(target, obj, null, callback);
    });
};