根据官方文档，我们知道axios支持nodejs、浏览器环境，但不支持uniapp、小程序，所以要想在uniapp中使用axios就要自定义实现。axios文档对自定义实现，作了说明。

// `adapter` allows custom handling of requests which makes testing easier.
  // Return a promise and supply a valid response (see lib/adapters/README.md).
  adapter: function (config) {
    
    /* ... */
  },

翻译过来就是，要想自定义实现，就要覆盖adapter方法，默认实现如下

var settle = require('./../core/settle');

module.exports = function myAdapter(config) {
    
  // At this point:
  //  - config has been merged with defaults
  //  - request transformers have already run
  //  - request interceptors have already run
  
  // Make the request using config provided
  // Upon response settle the Promise

  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);

    // From here:
    //  - response transformers will run
    //  - response interceptors will run
  });
}

settle.js中的代码

'use strict';

import AxiosError from './AxiosError.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.
 *
 * @returns {object} The response.
 */
export default function settle(resolve, reject, response) {
  const validateStatus = response.config.validateStatus;
  if (!response.status || !validateStatus || validateStatus(response.status)) {
    resolve(response);
  } else {
    reject(new AxiosError(
      'Request failed with status code ' + response.status,
      [AxiosError.ERR_BAD_REQUEST, AxiosError.ERR_BAD_RESPONSE][Math.floor(response.status / 100) - 4],
      response.config,
      response.request,
      response
    ));
  }
}

结合uniapp的api，可对axios如此封装

let count = 0
axios.defaults.adapter = function(config) {
     //自己定义个适配器，用来适配uniapp的语法
  count++
  if (count == 1) {
    
    uni.showLoading({
    
      title: "加载中",
	  mask:true
    })
  }
  return new Promise((resolve, reject) => {
    
    var settle = require('axios/lib/core/settle');
    var buildURL = require('axios/lib/helpers/buildURL');
    uni.request({
    
      method: config.method.toUpperCase(),
      url: config.baseURL + config.url,
      header: config.headers,
      data: config.data,
      dataType: config.dataType,
      responseType: config.responseType,
      sslVerify: config.sslVerify,
      complete: function complete(response) {
    
        count--
        if (count == 0) {
    
          uni.hideLoading()
        }
        if (response.data.code != 200) {
    
          uni.showToast({
    
            title: response.data.msg,
            duration: 5000,
            icon: 'none'
          })
          reject(response.data.msg)
          return
        }
        response = {
    
          data: response.data,
          status: response.statusCode,
          errMsg: response.errMsg,
          header: response.header,
          config: config
        };
        settle(resolve, reject, response);
      }
    })
  })
}

我们不禁要问，直接用uni.request封装请求不更简单吗？比如，

function request(data){
    
 return new Promise((resolve,reject)=>{
    
		uni.request({
    
			data,
			complete:function(response){
    
			 resolve(response);
			}
	 })
 })
}

这样做是可以，但没有了拦截器、baseUrl、参数转换等功能；基于axios封装，可以使用axios的api，比如拦截器。

// 添加请求拦截器
axios.interceptors.request.use(function (config) {
    
    // 在发送请求之前做些什么
    return config;
  }, function (error) {
    
    // 对请求错误做些什么
    return Promise.reject(error);
  });

// 添加响应拦截器
axios.interceptors.response.use(function (response) {
    
    // 2xx 范围内的状态码都会触发该函数。
    // 对响应数据做点什么
    return response;
  }, function (error) {
    
    // 超出 2xx 范围的状态码都会触发该函数。
    // 对响应错误做点什么
    return Promise.reject(error);
  });

总结

• uniapp中使用axios，是为了按照axios的风格来发送请求，并且axios提供了请求拦截器、响应拦截器、baseUrl、请求参数自动转换等功能；否则就要自己实现；
• 通过axios开放的adapter方法来适配uniapp环境，uniapp中发送去请求的api是uni.request。