axios源码解析（二）核心

核心函数

核心工具函数 core/*.js

1.buildFullPath.js

用于将baseURL与请求的requestURL拼接

module.exports = function buildFullPath(baseURL, requestedURL) {
  if (baseURL && !isAbsoluteURL(requestedURL)) {
    return combineURLs(baseURL, requestedURL);
  }
  return requestedURL;
};

2.createError.js和 enhanceError.js

module.exports = function createError(message, config, code, request, response) {
  var error = new Error(message);
  return enhanceError(error, config, code, request, response);
};

/**
 * Update an Error with the specified config, error code, and response.
 *
 * @param {Error} error The error to update.
 * @param {Object} config The config.
 * @param {string} [code] The error code (for example, 'ECONNABORTED').
 * @param {Object} [request] The request.
 * @param {Object} [response] The response.
 * @returns {Error} The error.
 */
module.exports = function enhanceError(error, config, code, request, response) {
  error.config = config;
  if (code) {
    error.code = code;
  }

  error.request = request;
  error.response = response;
  error.isAxiosError = true;

  error.toJSON = function() {
    return {
      // Standard
      message: this.message,
      name: this.name,
      // Microsoft
      description: this.description,
      number: this.number,
      // Mozilla
      fileName: this.fileName,
      lineNumber: this.lineNumber,
      columnNumber: this.columnNumber,
      stack: this.stack,
      // Axios
      config: this.config,
      code: this.code
    };
  };
  return error;
};

这两个函数主要用于打印错误信息，着重注意一下，toJSON函数

3.用于处理数据转换的函数 transformData.js

/**
 * Transform the data for a request or a response
 *
 * @param {Object|String} data The data to be transformed
 * @param {Array} headers The headers for the request or response
 * @param {Array|Function} fns A single function or Array of functions
 * @returns {*} The resulting transformed data
 */
module.exports = function transformData(data, headers, fns) {
  /*eslint no-param-reassign:0*/
  utils.forEach(fns, function transform(fn) {
    data = fn(data, headers);
  });

  return data;
};

在发送请求前会调用此函数，此函依次使用transformRequest数组中的每个函数来处理data，第一个的输出作为第二个的输入，将最后结果返回。

4.用于合并配置的mergeConfig.js函数

/**
 * Config-specific merge-function which creates a new config-object
 * by merging two configuration objects together.
 *
 * @param {Object} config1
 * @param {Object} config2
 * @returns {Object} New object resulting from merging config2 to config1
 */
module.exports = function mergeConfig(config1, config2) {
  // eslint-disable-next-line no-param-reassign
  config2 = config2 || {};
  var config = {};

  var valueFromConfig2Keys = ['url', 'method', 'params', 'data'];
  var mergeDeepPropertiesKeys = ['headers', 'auth', 'proxy'];
  var defaultToConfig2Keys = [
    'baseURL', 'url', 'transformRequest', 'transformResponse', 'paramsSerializer',
    'timeout', 'withCredentials', 'adapter', 'responseType', 'xsrfCookieName',
    'xsrfHeaderName', 'onUploadProgress', 'onDownloadProgress',
    'maxContentLength', 'validateStatus', 'maxRedirects', 'httpAgent',
    'httpsAgent', 'cancelToken', 'socketPath'
  ];

  utils.forEach(valueFromConfig2Keys, function valueFromConfig2(prop) {
    if (typeof config2[prop] !== 'undefined') {
      config[prop] = config2[prop];
    }
  });

  utils.forEach(mergeDeepPropertiesKeys, function mergeDeepProperties(prop) {
    if (utils.isObject(config2[prop])) {
      config[prop] = utils.deepMerge(config1[prop], config2[prop]);
    } else if (typeof config2[prop] !== 'undefined') {
      config[prop] = config2[prop];
    } else if (utils.isObject(config1[prop])) {
      config[prop] = utils.deepMerge(config1[prop]);
    } else if (typeof config1[prop] !== 'undefined') {
      config[prop] = config1[prop];
    }
  });

  utils.forEach(defaultToConfig2Keys, function defaultToConfig2(prop) {
    if (typeof config2[prop] !== 'undefined') {
      config[prop] = config2[prop];
    } else if (typeof config1[prop] !== 'undefined') {
      config[prop] = config1[prop];
    }
  });

  var axiosKeys = valueFromConfig2Keys
    .concat(mergeDeepPropertiesKeys)
    .concat(defaultToConfig2Keys);

  var otherKeys = Object
    .keys(config2)
    .filter(function filterAxiosKeys(key) {
      return axiosKeys.indexOf(key) === -1;
    });

  utils.forEach(otherKeys, function otherKeysDefaultToConfig2(prop) {
    if (typeof config2[prop] !== 'undefined') {
      config[prop] = config2[prop];
    } else if (typeof config1[prop] !== 'undefined') {
      config[prop] = config1[prop];
    }
  });

  return config;
};

5.settle.js

/**
 * Resolve or reject a Promise based on response status.
 *
 * @param {Function} resolve A function that resolves the promise.
 * @param {Function} reject A function that rejects the promise.
 * @param {object} response The response.
 */
module.exports = function settle(resolve, reject, response) {
  var validateStatus = response.config.validateStatus;
  if (!validateStatus || validateStatus(response.status)) {
    resolve(response);

    
  } else {
    reject(createError(
      'Request failed with status code ' + response.status,
      response.config,
      null,
      response.request,
      response
    ));
  }
};

6.dispatchRequest.js

/**
 * Throws a `Cancel` if cancellation has been requested.
 */
function throwIfCancellationRequested(config) {
  if (config.cancelToken) {
    config.cancelToken.throwIfRequested();
  }
}

/**
 * Dispatch a request to the server using the configured adapter.
 *
 * @param {object} config The config that is to be used for the request
 * @returns {Promise} The Promise to be fulfilled
 */
module.exports = function dispatchRequest(config) {
  throwIfCancellationRequested(config);

  // Ensure headers exist
  config.headers = config.headers || {};

  // Transform request data
  config.data = transformData(
    config.data,
    config.headers,
    config.transformRequest
  );

  // Flatten headers
  config.headers = utils.merge(
    config.headers.common || {},
    config.headers[config.method] || {},
    config.headers || {}
  );

  utils.forEach(
    ['delete', 'get', 'head', 'post', 'put', 'patch', 'common'],
    function cleanHeaderConfig(method) {
      delete config.headers[method];
    }
  );

  var adapter = config.adapter || defaults.adapter;

  return adapter(config).then(function onAdapterResolution(response) {
    throwIfCancellationRequested(config);

    // Transform response data
    response.data = transformData(
      response.data,
      response.headers,
      config.transformResponse
    );

    return response;
  }, function onAdapterRejection(reason) {
    if (!isCancel(reason)) {
      throwIfCancellationRequested(config);

      // Transform response data
      if (reason && reason.response) {
        reason.response.data = transformData(
          reason.response.data,
          reason.response.headers,
          config.transformResponse
        );
      }
    }

    return Promise.reject(reason);
  });
};

7.InterceptorManager.js

function InterceptorManager() {
  this.handlers = [];
}

/**
 * Add a new interceptor to the stack
 *
 * @param {Function} fulfilled The function to handle `then` for a `Promise`
 * @param {Function} rejected The function to handle `reject` for a `Promise`
 *
 * @return {Number} An ID used to remove interceptor later
 */
InterceptorManager.prototype.use = function use(fulfilled, rejected) {
  this.handlers.push({
    fulfilled: fulfilled,
    rejected: rejected
  });
  return this.handlers.length - 1;
};

/**
 * Remove an interceptor from the stack
 *
 * @param {Number} id The ID that was returned by `use`
 */
InterceptorManager.prototype.eject = function eject(id) {
  if (this.handlers[id]) {
    this.handlers[id] = null;
  }
};

/**
 * Iterate over all the registered interceptors
 *
 * This method is particularly useful for skipping over any
 * interceptors that may have become `null` calling `eject`.
 *
 * @param {Function} fn The function to call for each interceptor
 */
InterceptorManager.prototype.forEach = function forEach(fn) {
  utils.forEach(this.handlers, function forEachHandler(h) {
    if (h !== null) {
      fn(h);
    }
  });
};

module.exports = InterceptorManager;

8.Axios.js

/**
 * Create a new instance of Axios
 *
 * @param {Object} instanceConfig The default config for the instance
 */
function Axios(instanceConfig) {
  this.defaults = instanceConfig;
  this.interceptors = {
    request: new InterceptorManager(),
    response: new InterceptorManager()
  };
}

/**
 * Dispatch a request
 *
 * @param {Object} config The config specific for this request (merged with this.defaults)
 */
Axios.prototype.request = function request(config) {
  /*eslint no-param-reassign:0*/
  // Allow for axios('example/url'[, config]) a la fetch API
  if (typeof config === 'string') {
    config = arguments[1] || {};
    config.url = arguments[0];
  } else {
    config = config || {};
  }

  config = mergeConfig(this.defaults, config);

  // Set config.method
  if (config.method) {
    config.method = config.method.toLowerCase();
  } else if (this.defaults.method) {
    config.method = this.defaults.method.toLowerCase();
  } else {
    config.method = 'get';
  }

  // Hook up interceptors middleware
  var chain = [dispatchRequest, undefined];
  var promise = Promise.resolve(config);

  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);
  });

  while (chain.length) {
    promise = promise.then(chain.shift(), chain.shift());
  }

  return promise;
};

Axios.prototype.getUri = function getUri(config) {
  config = mergeConfig(this.defaults, config);
  return buildURL(config.url, config.params, config.paramsSerializer).replace(/^\?/, '');
};

// Provide aliases for supported request methods
utils.forEach(['delete', 'get', 'head', 'options'], function forEachMethodNoData(method) {
  /*eslint func-names:0*/
  Axios.prototype[method] = function(url, config) {
    return this.request(utils.merge(config || {}, {
      method: method,
      url: url
    }));
  };
});

utils.forEach(['post', 'put', 'patch'], function forEachMethodWithData(method) {
  /*eslint func-names:0*/
  Axios.prototype[method] = function(url, data, config) {
    return this.request(utils.merge(config || {}, {
      method: method,
      url: url,
      data: data
    }));
  };
});

module.exports = Axios;

中断请求发送的cancel/*.js

cancel文件夹下的主要内容是负责ajax请求的拦截。

Cancel.js

function Cancel(message) {
  this.message = message;
}

Cancel.prototype.toString = function toString() {
  return 'Cancel' + (this.message ? ': ' + this.message : '');
};

Cancel.prototype.__CANCEL__ = true;

CancelToken.js

/**
 * A `CancelToken` is an object that can be used to request cancellation of an operation.
 *
 * @class
 * @param {Function} executor The executor function.
 */
function CancelToken(executor) {
  if (typeof executor !== 'function') {
    throw new TypeError('executor must be a function.');
  }

  var resolvePromise;
  this.promise = new Promise(function promiseExecutor(resolve) {
    resolvePromise = resolve;
  });

  var token = this;
  executor(function cancel(message) {
    if (token.reason) {
      // Cancellation has already been requested
      return;
    }

    token.reason = new Cancel(message);
    resolvePromise(token.reason);
  });
}

/**
 * Throws a `Cancel` if cancellation has been requested.
 */
CancelToken.prototype.throwIfRequested = function throwIfRequested() {
  if (this.reason) {
    throw this.reason;
  }
};

/**
 * Returns an object that contains a new `CancelToken` and a function that, when called,
 * cancels the `CancelToken`.
 */
CancelToken.source = function source() {
  var cancel;
  var token = new CancelToken(function executor(c) {
    cancel = c;
  });
  return {
    token: token,
    cancel: cancel
  };
};

isCancel.js

module.exports = function isCancel(value) {
  return !!(value && value.__CANCEL__);
};

在实际使用中主要使用的是CancelToken类

默认配置：default.js

'use strict';

var utils = require('./utils');
var normalizeHeaderName = require('./helpers/normalizeHeaderName');

var DEFAULT_CONTENT_TYPE = {
  'Content-Type': 'application/x-www-form-urlencoded'
};

function setContentTypeIfUnset(headers, value) {
  if (!utils.isUndefined(headers) && utils.isUndefined(headers['Content-Type'])) {
    headers['Content-Type'] = value;
  }
}

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 defaults = {
  adapter: getDefaultAdapter(),

  transformRequest: [function transformRequest(data, headers) {
    normalizeHeaderName(headers, 'Accept');
    normalizeHeaderName(headers, 'Content-Type');
    if (utils.isFormData(data) ||
      utils.isArrayBuffer(data) ||
      utils.isBuffer(data) ||
      utils.isStream(data) ||
      utils.isFile(data) ||
      utils.isBlob(data)
    ) {
      return data;
    }
    if (utils.isArrayBufferView(data)) {
      return data.buffer;
    }
    if (utils.isURLSearchParams(data)) {
      setContentTypeIfUnset(headers, 'application/x-www-form-urlencoded;charset=utf-8');
      return data.toString();
    }
    if (utils.isObject(data)) {
      setContentTypeIfUnset(headers, 'application/json;charset=utf-8');
      return JSON.stringify(data);
    }
    return data;
  }],

  transformResponse: [function transformResponse(data) {
    /*eslint no-param-reassign:0*/
    if (typeof data === 'string') {
      try {
        data = JSON.parse(data);
      } catch (e) { /* Ignore */ }
    }
    return data;
  }],

  /**
   * A timeout in milliseconds to abort a request. If set to 0 (default) a
   * timeout is not created.
   */
  timeout: 0,

  xsrfCookieName: 'XSRF-TOKEN',
  xsrfHeaderName: 'X-XSRF-TOKEN',

  maxContentLength: -1,

  validateStatus: function validateStatus(status) {
    return status >= 200 && status < 300;
  }
};

defaults.headers = {
  common: {
    'Accept': 'application/json, text/plain, */*'
  }
};

utils.forEach(['delete', 'get', 'head'], function forEachMethodNoData(method) {
  defaults.headers[method] = {};
});

utils.forEach(['post', 'put', 'patch'], function forEachMethodWithData(method) {
  defaults.headers[method] = utils.merge(DEFAULT_CONTENT_TYPE);
});

module.exports = defaults;

此函数主要用于获取默认的配置信息，其中transformRequest可以着重看下，看下是怎么处理data的。

 // `data` 是作为请求主体被发送的数据
  // 只适用于这些请求方法 'PUT', 'POST', 和 'PATCH'
  // 在没有设置 `transformRequest` 时，必须是以下类型之一：
  // - string, plain object, ArrayBuffer, ArrayBufferView, URLSearchParams
  // - 浏览器专属：FormData, File, Blob
  // - Node 专属： Stream

入口文件axios.js

/**
 * Create an instance of Axios
 *
 * @param {Object} defaultConfig The default config for the instance
 * @return {Axios} A new instance of Axios
 */
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);

// Expose Axios class to allow class inheritance
axios.Axios = Axios;

// Factory for creating new instances
axios.create = function create(instanceConfig) {
  return createInstance(mergeConfig(axios.defaults, instanceConfig));
};

axios.Cancel = require('./cancel/Cancel');
axios.CancelToken = require('./cancel/CancelToken');
axios.isCancel = require('./cancel/isCancel');

axios.all = function all(promises) {
  return Promise.all(promises);
};
axios.spread = require('./helpers/spread');

module.exports = axios;

module.exports.default = axios;

发送请求核心的adapter/*.js

此文件夹内的文件是框架的核心，主要用于实际发送请求，分为浏览器平台的xhr.js和node平台的http.js

xhr.js

module.exports = function xhrAdapter(config) {
  return new Promise(function dispatchXhrRequest(resolve, reject) {
    var requestData = config.data;
    var requestHeaders = config.headers;

    if (utils.isFormData(requestData)) {
      delete requestHeaders['Content-Type']; // Let the browser set it
    }

    var request = new XMLHttpRequest();

    // HTTP basic authentication
    if (config.auth) {
      var username = config.auth.username || '';
      var password = config.auth.password || '';
      requestHeaders.Authorization = 'Basic ' + btoa(username + ':' + password);
    }

    var fullPath = buildFullPath(config.baseURL, config.url);
    request.open(config.method.toUpperCase(), buildURL(fullPath, config.params, config.paramsSerializer), true);

    // Set the request timeout in MS
    request.timeout = config.timeout;

    // Listen for ready state
    request.onreadystatechange = function handleLoad() {
      if (!request || request.readyState !== 4) {
        return;
      }

      // The request errored out and we didn't get a response, this will be
      // handled by onerror instead
      // With one exception: request that using file: protocol, most browsers
      // will return status as 0 even though it's a successful request
      if (request.status === 0 && !(request.responseURL && request.responseURL.indexOf('file:') === 0)) {
        return;
      }

      // Prepare the response
      var responseHeaders = 'getAllResponseHeaders' in request ? parseHeaders(request.getAllResponseHeaders()) : null;
      var responseData = !config.responseType || config.responseType === 'text' ? request.responseText : request.response;
      var response = {
        data: responseData,
        status: request.status,
        statusText: request.statusText,
        headers: responseHeaders,
        config: config,
        request: request
      };

      settle(resolve, reject, response);

      // Clean up request
      request = null;
    };

    // Handle browser request cancellation (as opposed to a manual cancellation)
    request.onabort = function handleAbort() {
      if (!request) {
        return;
      }

      reject(createError('Request aborted', config, 'ECONNABORTED', request));

      // Clean up request
      request = null;
    };

    // Handle low level network errors
    request.onerror = function handleError() {
      // Real errors are hidden from us by the browser
      // onerror should only fire if it's a network error
      reject(createError('Network Error', config, null, request));

      // Clean up request
      request = null;
    };

    // Handle timeout
    request.ontimeout = function handleTimeout() {
      reject(createError('timeout of ' + config.timeout + 'ms exceeded', config, 'ECONNABORTED',
        request));

      // Clean up request
      request = null;
    };

    // Add xsrf header
    // This is only done if running in a standard browser environment.
    // Specifically not if we're in a web worker, or react-native.
    if (utils.isStandardBrowserEnv()) {
      var cookies = require('./../helpers/cookies');

      // Add xsrf header
      var xsrfValue = (config.withCredentials || isURLSameOrigin(fullPath)) && config.xsrfCookieName ?
        cookies.read(config.xsrfCookieName) :
        undefined;

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

    // Add headers to the request
    if ('setRequestHeader' in request) {
      utils.forEach(requestHeaders, function setRequestHeader(val, key) {
        if (typeof requestData === 'undefined' && key.toLowerCase() === 'content-type') {
          // Remove Content-Type if data is undefined
          delete requestHeaders[key];
        } else {
          // Otherwise add header to the request
          request.setRequestHeader(key, val);
        }
      });
    }

    // Add withCredentials to request if needed
    if (config.withCredentials) {
      request.withCredentials = true;
    }

    // Add responseType to request if needed
    if (config.responseType) {
      try {
        request.responseType = config.responseType;
      } catch (e) {
        // Expected DOMException thrown by browsers not compatible XMLHttpRequest Level 2.
        // But, this can be suppressed for 'json' type as it can be parsed by default 'transformResponse' function.
        if (config.responseType !== 'json') {
          throw e;
        }
      }
    }

    // Handle progress if needed
    if (typeof config.onDownloadProgress === 'function') {
      request.addEventListener('progress', config.onDownloadProgress);
    }

    // Not all browsers support upload events
    if (typeof config.onUploadProgress === 'function' && request.upload) {
      request.upload.addEventListener('progress', config.onUploadProgress);
    }

    if (config.cancelToken) {
      // Handle cancellation
      config.cancelToken.promise.then(function onCanceled(cancel) {
        if (!request) {
          return;
        }

        request.abort();
        reject(cancel);
        // Clean up request
        request = null;
      });
    }

    if (requestData === undefined) {
      requestData = null;
    }

    // Send the request
    request.send(requestData);
  });
};

浏览器中发送请求代码的逻辑很清晰。基本是包装了原生XMLHttpRequest对象的基本方法和属性。注意一下拦截的实现即可。

axios.js的

while (chain.length) {
    promise = promise.then(chain.shift(), chain.shift());
  }