axios原理和实现（GitHub上77.9K的Axios项目有哪些值得借鉴的地方详析）

// 添加请求拦截器
axios.interceptors.request.use(function (config) {
  config.headers.token = 'added by interceptor';
  return config;
});

// 添加响应拦截器
axios.interceptors.response.use(function (data) {
  data.data = data.data + ' - modified by interceptor';
  return data;
});

// lib/axios.js
function createInstance(defaultConfig) {
  var context = new Axios(defaultConfig);
  var instance = bind(Axios.prototype.request, context);

  // Copy axios.prototype to instance
  utils.extend(instance, Axios.prototype, context);
  // Copy context to instance
  utils.extend(instance, context);
  return instance;
}

// Create the default instance to be exported
var axios = createInstance(defaults);

// lib/core/Axios.js
function Axios(instanceConfig) {
  this.defaults = instanceConfig;
  this.interceptors = {
    request: new InterceptorManager(),
    response: new InterceptorManager()
  };
}

// lib/core/InterceptorManager.js
function InterceptorManager() {
  this.handlers = [];
}

InterceptorManager.prototype.use = function use(fulfilled, rejected) {
  this.handlers.push({
    fulfilled: fulfilled,
    rejected: rejected
  });
  // 返回当前的索引，用于移除已注册的拦截器
  return this.handlers.length - 1;
};

axios({
  url: '/hello',
  method: 'get',
}).then(res =>{
  console.log('axios res: ', res)
  console.log('axios res.data: ', res.data)
})

// lib/core/Axios.js
Axios.prototype.request = function request(config) {
  config = mergeConfig(this.defaults, config);

  // 省略部分代码
  var chain = [dispatchRequest, undefined];
  var promise = Promise.resolve(config);

  // 任务编排
  this.interceptors.request.forEach(function unshiftRequestInterceptors(interceptor) {
    chain.unshift(interceptor.fulfilled, interceptor.rejected);
  });

  this.interceptors.response.forEach(function pushResponseInterceptors(interceptor) {
    chain.push(interceptor.fulfilled, interceptor.rejected);
  });

  // 任务调度
  while (chain.length) {
    promise = promise.then(chain.shift(), chain.shift());
  }

  return promise;
};

 // lib/core/Axios.js
Axios.prototype.request = function request(config) {
  // 省略部分代码
  var promise = Promise.resolve(config);
  while (chain.length) {
    promise = promise.then(chain.shift(), chain.shift());
  }
}

// 添加请求拦截器 —— 处理请求配置对象
axios.interceptors.request.use(function (config) {
  config.headers.token = 'added by interceptor';
  return config;
});

// 添加响应拦截器 —— 处理响应对象
axios.interceptors.response.use(function (data) {
  data.data = data.data + ' - modified by interceptor';
  return data;
});

axios({
  url: '/hello',
  method: 'get',
}).then(res =>{
  console.log('axios res.data: ', res.data)
})

// lib/core/dispatchRequest.js
module.exports = function dispatchRequest(config) {
  // 省略部分代码
  var adapter = config.adapter || defaults.adapter;
  
  return adapter(config).then(function onAdapterResolution(response) {
    // 省略部分代码
    return response;
  }, function onAdapterRejection(reason) {
    // 省略部分代码
    return Promise.reject(reason);
  });
};

// lib/defaults.js
var defaults = {
  adapter: getDefaultAdapter(),
  xsrfCookieName: 'XSRF-TOKEN',
  xsrfHeaderName: 'X-XSRF-TOKEN',
  //...
}

function getDefaultAdapter() {
  var adapter;
  if (typeof XMLHttpRequest !== 'undefined') {
    // For browsers use XHR adapter
    adapter = require('./adapters/xhr');
  } else if (typeof process !== 'undefined' && 
    Object.prototype.toString.call(process) === '[object process]') {
    // For node use HTTP adapter
    adapter = require('./adapters/http');
  }
  return adapter;
}

var settle = require('./../core/settle');
module.exports = function myAdapter(config) {
  // 当前时机点：
  //  - config配置对象已经与默认的请求配置合并
  //  - 请求转换器已经运行
  //  - 请求拦截器已经运行
  
  // 使用提供的config配置对象发起请求
  // 根据响应对象处理Promise的状态
  return new Promise(function(resolve, reject) {
    var response = {
      data: responseData,
      status: request.status,
      statusText: request.statusText,
      headers: responseHeaders,
      config: config,
      request: request
    };

    settle(resolve, reject, response);

    // 此后:
    //  - 响应转换器将会运行
    //  - 响应拦截器将会运行
  });
}

var axios = require("axios");
var MockAdapter = require("axios-mock-adapter");

// 在默认的Axios实例上设置mock适配器
var mock = new MockAdapter(axios);

// 模拟 GET /users 请求
mock.onGet("/users").reply(200, {
  users: [{ id: 1, name: "John Smith" }],
});

axios.get("/users").then(function (response) {
  console.log(response.data);
});

<form method="POST" action="/upload?_csrf={{由服务端生成}}" enctype="multipart/form-data">
  用户名: <input name="name" />
  选择头像: <input name="file" type="file" />
  <button type="submit">提交</button>
</form>

let csrfToken = Cookies.get('csrfToken');

function csrfSafeMethod(method) {
  // 以下HTTP方法不需要进行CSRF防护
  return (/^(GET|HEAD|OPTIONS|TRACE)$/.test(method));
}

$.ajaxSetup({
  beforeSend: function(xhr, settings) {
    if (!csrfSafeMethod(settings.type) && !this.crossDomain) {
      xhr.setRequestHeader('x-csrf-token', csrfToken);
    }
  },
});

// lib/defaults.js
var defaults = {
  adapter: getDefaultAdapter(),

  // 省略部分代码
  xsrfCookieName: 'XSRF-TOKEN',
  xsrfHeaderName: 'X-XSRF-TOKEN',
};

// lib/adapters/xhr.js
module.exports = function xhrAdapter(config) {
  return new Promise(function dispatchXhrRequest(resolve, reject) {
    var requestHeaders = config.headers;
    
    var request = new XMLHttpRequest();
    // 省略部分代码
    
    // 添加xsrf头部
    if (utils.isStandardBrowserEnv()) {
      var xsrfValue = (config.withCredentials || isURLSameOrigin(fullPath)) && config.xsrfCookieName ?
        cookies.read(config.xsrfCookieName) :
        undefined;

      if (xsrfValue) {
        requestHeaders[config.xsrfHeaderName] = xsrfValue;
      }
    }

    request.send(requestData);
  });
};