一比一还原axios源码（五）—— 拦截器「建议收藏」

axios.interceptors.request.use((config) => {
  config.headers.test += "1";
  return config;
});
axios.interceptors.request.use((config) => {
  config.headers.test += "2";
  return config;
});
axios.interceptors.request.use((config) => {
  config.headers.test += "3";
  return config;
});

axios.interceptors.response.use((res) => {
  res.data += "1";
  return res;
});
let c5 = axios.interceptors.response.use((res) => {
  res.data += "2";
  return res;
});
axios.interceptors.response.use((res) => {
  res.data += "3";
  return res;
});

axios.interceptors.response.eject(c5);

axios({
  url: "/c5/get",
  method: "get",
  headers: {
    test: "",
  },
}).then((res) => {
  console.log(res.data);
});

"use strict";

import utils from "./../utils";

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, options) {
  this.handlers.push({
    fulfilled: fulfilled,
    rejected: rejected,
    synchronous: options ? options.synchronous : false,
    runWhen: options ? options.runWhen : null,
  });
  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);
    }
  });
};

export default InterceptorManager;

Axios.prototype.request = function (configOrUrl, config) { if (typeof configOrUrl === "string") { if (!config) { config = {}; } config.url = configOrUrl; } else { config = configOrUrl; } // 请求拦截器调用链 var requestInterceptorChain = []; // 是否同步 var synchronousRequestInterceptors = true; // 通过拦截器的forEach方法，通过回调函数的方式，把所有的请求拦截放到requestInterceptorChain数组里 this.interceptors.request.forEach(function unshiftRequestInterceptors( interceptor ) { if ( // 判断下如果runWhen是false就return掉了 typeof interceptor.runWhen === "function" && interceptor.runWhen(config) === false ) { return; } // 判断是否是同步执行 synchronousRequestInterceptors = synchronousRequestInterceptors && interceptor.synchronous; // 把两个回调函数放到数组的头部 // 注意这里不是unshift一个数组，而是独立的，就是这样[interceptor.fulfilled,interceptor.rejected] // [3,2,1]  requestInterceptorChain.unshift( interceptor.fulfilled, interceptor.rejected ); }); // 响应拦截器调用链 var responseInterceptorChain = []; // response这个比较简单，直接push进数组就完事了 this.interceptors.response.forEach(function pushResponseInterceptors( interceptor ) { responseInterceptorChain.push(interceptor.fulfilled, interceptor.rejected); }); // 定一个promise变量，后面用 var promise; // 如果不是同步的 if (!synchronousRequestInterceptors) { var chain = [dispatchRequest, undefined]; // 这块呢，就把整个requestInterceptorChain放到chain的前面  Array.prototype.unshift.apply(chain, requestInterceptorChain); // 这个就是把responseInterceptorChain放到[requestInterceptorChain,chain]后面 chain = chain.concat(responseInterceptorChain); // 额外要说的是到了这里，这个chain数组是什么样的呢 // 我们打印下,以我们之前的例子代码为例： // 它实际上是这样的[fn,undefined,fn,undefined,fn,undefined,fn,undefined,fn,undefined,fn,undefined] // 具体点，[requestInterceptorChain,chain,responseInterceptorChain] // 再具体点：[requestResolve3,undefined,requestResolve2,undefined,requestResolve1,undefined,dispatchRequest, undefined,responseResolve1,undefined,responseResolve3,undefined] console.log(chain, "chian"); // 这块可能就优点疑惑了，首先promise变量变成了一个已经resolved的Promise，resolve出去的就是config配置 promise = Promise.resolve(config); while (chain.length) { // 所以这里的then里面就是这样(resolve，reject) // 注意then方法的第二个参数就是reject的。 // 换句话说，这里就形成了一个一个的链式调用，源头是一个已经resolved的promise。 promise = promise.then(chain.shift(), chain.shift()); } // 返回咯 return promise; } // 那如果是同步的话，走下面的代码 // 很简单，就是同步执行罢了，我就不说了哦。 var newConfig = config; while (requestInterceptorChain.length) { var onFulfilled = requestInterceptorChain.shift(); var onRejected = requestInterceptorChain.shift(); try { // 新的config就是onFulfilled同步函数执行的结果，一步一步往下传 newConfig = onFulfilled(newConfig); } catch (error) { onRejected(error); break; } } // 执行dispatchRequest返回个promise，dispatchRequest本身就会返回promise，对吧？ try { promise = dispatchRequest(newConfig); } catch (error) { return Promise.reject(error); } // 循环执行responseInterceptorChain链。 while (responseInterceptorChain.length) { promise = promise.then( responseInterceptorChain.shift(), responseInterceptorChain.shift() ); } // 返回，结束 return promise; };