Axios

1.Json-server的搭建

官网：https://github.com/typicode/json-server

三步走

第一步：命令行安卓Json-server

npm install json-server

第二布：在对应文件夹下创建db.json的文件，内容如下：

{"posts": [{ "id": "1", "title": "a title", "views": 100 },{ "id": "2", "title": "another title", "views": 200 }],"comments": [{ "id": "1", "text": "a comment about post 1", "postId": "1" },{ "id": "2", "text": "another comment about post 1", "postId": "1" }],"profile": {"name": "typicode"}
}

第三步：在命令行启动服务

$ npx json-server db.json

如上便启动成功

点击对应的连接我们可以得到对应的Json字符串的数据

2.Axios的基本使用

官网：https://github.com/axios/axios

练习阶段采用链接引入方式：https://www.bootcdn.cn/axios/

通过四个按钮实现对db.json里面的数据的修改

1.发送Get请求

//第一个btns[0].onclick = function () {//发送AJAX请求axios({//请求类型method: 'GET',//URLurl: 'http://localhost:3000/posts/2'}).then((responce) => {console.log(responce);})}

url里的路径要写出对应的id号才能请求出对应的数据

2.添加新数据

//添加一篇新的文章btns[1].onclick = function () {//发送AJAX请求axios({//请求类型method: 'POST',//URLurl: 'http://localhost:3000/posts',//设置请求体data: {id: '3',titile: '祝我找到实习',views: 999}}).then((responce) => {console.log(responce);})}

​ 添加新数据需要设置请求体，在里面写出要添加的数据，点击玩按钮后可以按F12在网络里看是否请求成功，再回到db.json里我们就可以看到新的数据了。

​ 但这里有一个问题，我看视频里老师在请求体里是不用写对应的id的，但如果我不写的话，新添加的数据对应的id是一段看不懂的字符串，并不是字符串3，所以我在这里自己对数据设定了id

3.更新数据

btns[2].onclick = function () {//发送AJAX请求axios({//请求类型method: 'PUT',//URLurl: 'http://localhost:3000/posts/3',//设置请求体data: {titile: '我一定能找到实习',views: 999999}}).then((responce) => {console.log(responce);})}

更新数据也要在url里写出要更新的数据所对应的id号，并在请求体里写出你想修改的数据即可

4.删除数据

btns[3].onclick = function () {//发送AJAX请求axios({//请求类型method: 'delete',//URLurl: 'http://localhost:3000/posts/3',}).then((responce) => {console.log(responce);})}

删除数据同理，删除对应id号的数据

3.Axios的其他使用

除了像上述那样发送axios请求之外，我们还可以使用axios自带的方法来发送请求

下面用request和post来简单举个例子

//发送get请求btns[0].onclick = function () {axios.request({method: 'GET',url: 'http://localhost:3000/comments'}).then((result) => {console.log(result);})}//发送post请求btns[1].onclick = function () {axios.post(//对应的url'http://localhost:3000/comments',//想要添加的数据{text: '前端之大，一锅装不下',postId: '2'}).then((result) => {console.log(result);})}

写法基本上和上面的基本使用区别不大

4.Axios响应结果的结构分析

当我们发送一个axios请求的时候，其请求响应的结果如上所述，下面我们来简单分析一下里面每个属性的含义

• config：配置对象，包含了诸如请求类型、请求url、请求体等属性都可以在config里面找到
• data：响应体的结果，即服务器返回的结果，至于这里为什么返回的是一个对象，那是因为axios自动将服务器返回的结果进行了JSON解析，把他转成了一个对象，方便我们对于结果来进行一个处理
• headers：响应的头信息
• request：原生的AJAX请求对象，我们知道axios是用来发送Ajax请求，而发送Ajax请求就要用到我们底层的XMLHttpRequest的实例对象，而request这个属性保存的就是当前axios在发送请求时所创建的哪个Ajax请求对象，也就是XMLHttpRequest实例对象
• status：响应状态码
• statusText：响应的状态字符串

5.Axios配置对象详细说明

但凡提到config这个参数的，其实指的都是配置对象，现在我们来看看里面可以设置那些内容

{// `url` is the server URL that will be used for the requesturl: '/user',// `method` is the request method to be used when making the requestmethod: 'get', // default// `baseURL` will be prepended to `url` unless `url` is absolute.// It can be convenient to set `baseURL` for an instance of axios to pass relative URLs// to methods of that instance.baseURL: 'https://some-domain.com/api/',// `transformRequest` allows changes to the request data before it is sent to the server// This is only applicable for request methods 'PUT', 'POST', 'PATCH' and 'DELETE'// The last function in the array must return a string or an instance of Buffer, ArrayBuffer,// FormData or Stream// You may modify the headers object.transformRequest: [function (data, headers) {// Do whatever you want to transform the datareturn data;}],// `transformResponse` allows changes to the response data to be made before// it is passed to then/catchtransformResponse: [function (data) {// Do whatever you want to transform the datareturn data;}],// `headers` are custom headers to be sentheaders: {'X-Requested-With': 'XMLHttpRequest'},// `params` are the URL parameters to be sent with the request// Must be a plain object or a URLSearchParams objectparams: {ID: 12345},// `paramsSerializer` is an optional function in charge of serializing `params`// (e.g. https://www.npmjs.com/package/qs, http://api.jquery.com/jquery.param/)paramsSerializer: function (params) {return Qs.stringify(params, {arrayFormat: 'brackets'})},// `data` is the data to be sent as the request body// Only applicable for request methods 'PUT', 'POST', 'DELETE , and 'PATCH'// When no `transformRequest` is set, must be of one of the following types:// - string, plain object, ArrayBuffer, ArrayBufferView, URLSearchParams// - Browser only: FormData, File, Blob// - Node only: Stream, Bufferdata: {firstName: 'Fred'},// syntax alternative to send data into the body// method post// only the value is sent, not the keydata: 'Country=Brasil&City=Belo Horizonte',// `timeout` specifies the number of milliseconds before the request times out.// If the request takes longer than `timeout`, the request will be aborted.timeout: 1000, // default is `0` (no timeout)// `withCredentials` indicates whether or not cross-site Access-Control requests// should be made using credentialswithCredentials: false, // default// `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) {/* ... */},// `auth` indicates that HTTP Basic auth should be used, and supplies credentials.// This will set an `Authorization` header, overwriting any existing// `Authorization` custom headers you have set using `headers`.// Please note that only HTTP Basic auth is configurable through this parameter.// For Bearer tokens and such, use `Authorization` custom headers instead.auth: {username: 'janedoe',password: 's00pers3cret'},// `responseType` indicates the type of data that the server will respond with// options are: 'arraybuffer', 'document', 'json', 'text', 'stream'//   browser only: 'blob'responseType: 'json', // default// `responseEncoding` indicates encoding to use for decoding responses (Node.js only)// Note: Ignored for `responseType` of 'stream' or client-side requestsresponseEncoding: 'utf8', // default// `xsrfCookieName` is the name of the cookie to use as a value for xsrf tokenxsrfCookieName: 'XSRF-TOKEN', // default// `xsrfHeaderName` is the name of the http header that carries the xsrf token valuexsrfHeaderName: 'X-XSRF-TOKEN', // default// `onUploadProgress` allows handling of progress events for uploads// browser onlyonUploadProgress: function (progressEvent) {// Do whatever you want with the native progress event},// `onDownloadProgress` allows handling of progress events for downloads// browser onlyonDownloadProgress: function (progressEvent) {// Do whatever you want with the native progress event},// `maxContentLength` defines the max size of the http response content in bytes allowed in node.jsmaxContentLength: 2000,// `maxBodyLength` (Node only option) defines the max size of the http request content in bytes allowedmaxBodyLength: 2000,// `validateStatus` defines whether to resolve or reject the promise for a given// HTTP response status code. If `validateStatus` returns `true` (or is set to `null`// or `undefined`), the promise will be resolved; otherwise, the promise will be// rejected.validateStatus: function (status) {return status >= 200 && status < 300; // default},// `maxRedirects` defines the maximum number of redirects to follow in node.js.// If set to 0, no redirects will be followed.maxRedirects: 21, // default// `beforeRedirect` defines a function that will be called before redirect.// Use this to adjust the request options upon redirecting,// to inspect the latest response headers,// or to cancel the request by throwing an error// If maxRedirects is set to 0, `beforeRedirect` is not used.beforeRedirect: (options, { headers }) => {if (options.hostname === "example.com") {options.auth = "user:password";}};// `socketPath` defines a UNIX Socket to be used in node.js.// e.g. '/var/run/docker.sock' to send requests to the docker daemon.// Only either `socketPath` or `proxy` can be specified.// If both are specified, `socketPath` is used.socketPath: null, // default// `httpAgent` and `httpsAgent` define a custom agent to be used when performing http// and https requests, respectively, in node.js. This allows options to be added like// `keepAlive` that are not enabled by default.httpAgent: new http.Agent({ keepAlive: true }),httpsAgent: new https.Agent({ keepAlive: true }),// `proxy` defines the hostname, port, and protocol of the proxy server.// You can also define your proxy using the conventional `http_proxy` and// `https_proxy` environment variables. If you are using environment variables// for your proxy configuration, you can also define a `no_proxy` environment// variable as a comma-separated list of domains that should not be proxied.// Use `false` to disable proxies, ignoring environment variables.// `auth` indicates that HTTP Basic auth should be used to connect to the proxy, and// supplies credentials.// This will set an `Proxy-Authorization` header, overwriting any existing// `Proxy-Authorization` custom headers you have set using `headers`.// If the proxy server uses HTTPS, then you must set the protocol to `https`. proxy: {protocol: 'https',host: '127.0.0.1',port: 9000,auth: {username: 'mikeymike',password: 'rapunz3l'}},// `cancelToken` specifies a cancel token that can be used to cancel the request// (see Cancellation section below for details)cancelToken: new CancelToken(function (cancel) {}),// an alternative way to cancel Axios requests using AbortControllersignal: new AbortController().signal,// `decompress` indicates whether or not the response body should be decompressed // automatically. If set to `true` will also remove the 'content-encoding' header // from the responses objects of all decompressed responses// - Node only (XHR cannot turn off decompression)decompress: true // default// `insecureHTTPParser` boolean.// Indicates where to use an insecure HTTP parser that accepts invalid HTTP headers.// This may allow interoperability with non-conformant HTTP implementations.// Using the insecure parser should be avoided.// see options https://nodejs.org/dist/latest-v12.x/docs/api/http.html#http_http_request_url_options_callback// see also https://nodejs.org/en/blog/vulnerability/february-2020-security-releases/#strict-http-header-parsing-noneinsecureHTTPParser: undefined // default// transitional options for backward compatibility that may be removed in the newer versionstransitional: {// silent JSON parsing mode// `true`  - ignore JSON parsing errors and set response.data to null if parsing failed (old behaviour)// `false` - throw SyntaxError if JSON parsing failed (Note: responseType must be set to 'json')silentJSONParsing: true, // default value for the current Axios version// try to parse the response string as JSON even if `responseType` is not 'json'forcedJSONParsing: true,// throw ETIMEDOUT error instead of generic ECONNABORTED on request timeoutsclarifyTimeoutError: false,},env: {// The FormData class to be used to automatically serialize the payload into a FormData objectFormData: window?.FormData || global?.FormData}
}

其中有几个注意点：

• baseURL是一个URL的基础结构，axios内部会自动将baseURL与url进行一个结合，形成最终的url结果。例如你可以将域名和协议写在baseURL中，而在url中直接写路径
• transformRequest可以对请求的数据进行一个处理，处理完之后，再将处理的结果发送给服务器。(对请求参数进行一个预处理)
• transformResponse可以对相应的数据进行处理，改变完之后我们再用自定义的回调去处理这个结果。(对响应参数进行一个预处理)
• headers对请求头信息进行一个配置
• params对url参数(准确的说是url里面的查询字符串)进行设置
• 例如：

axios({url: '/post',//post?a=100&b=200params: {a:100,b:200}

• data是请求体设置，有两种形式：对象形式和字符串形式。如果是对象形式，axios会将其转化为json形式字符串；如果是字符串形式，那么axios会直接传递
• timeout为超时时间，发送请求时如果超过时间则这个请求就会被取消。单位为毫秒
• withCredentials在跨域请求时对cookie的携带作一个设置。false为不携带，true则在跨域请求时可以携带cookie。
• adapter对请求的适配器进行设置
• responseType响应体结果的格式做一个设置，默认值是json
• responseEncoding响应结果的编码设置
• xsrfCookieName、xsrfHeaderName跨站请求的标识，对cookie的名字和头信息进行设置
• onUploadProgress在上传的时候做出的回调
• onDownloadProgress在下载的时候做出的回调
• maxContentLength设置http响应的最大尺寸，单位：字节
• maxBodyLength设置请求体的最大尺寸，单位：字节
• validateStatus对响应结果的成功进行一个设置。也就是说什么情况下才认定他是成功的。默认值为响应代码大于200，小于300.(status >= 200 && status < 300)，不用改
• maxRedirects设置最大跳转次数
• socketPath设定socket文件的位置。作用:向docker的守护进程发送请求。
• httpAgent、 httpsAgent对客户端的信息进行设置
• proxy设置代理
• cancelToken对AJAX请求做一个取消的设置
• decompress设置对响应结果是不是做一个解压。默认：解压

6.axios的默认配置

默认配置可以简单理解为我们对重复配置的统一的默认编写，后续再使用的时候就可以不用再重复配置相关的属性了

//获取按钮const btns = document.querySelectorAll('button')//设置默认配置axios.defaults.method = 'GET';//设置默认的请求类型为 GETaxios.defaults.baseURL = 'http://localhost:3000'//设置基础 URL//发送get请求btns[0].onclick = function () {axios({url: '/posts',params: {id: 100}}).then((result) => {console.log(result);})}

7.axios创建实例对象（create）

使用方法如下：

//创建实例对象
const a = axios.create({baseURL:'http://api/a.com'	//假设的一个urltimeout:2000
})
const b = axios.create({baseURL:'http://api/b.com'	//假设的一个urltimeout:2000
})
//这里的a和b与axios对象的功能几乎是一样的

那么创建实例对象有什么作用呢？

现在假设我们的项目，它的接口数据服务不是来在于单一的一个服务器，如果我们去使用默认配置去设置的话，那么我们只能实现一个服务器的接口数据，另一个又得重新配置该接口的相应的数据，这样想来也并不合适，所以这时候我们可以创建两个对象，如果我们要给a发送请求时，我们就去借助a对象来实现，同理b也一样

8.axios拦截器

1.请求拦截器

作用：在真正发请求前执行一个回调，做一些事情，比如追加请求头、追加参数、界面加载进度条的提示等等。一般来说只有一个回调

//请求拦截器：在发请求之前，请求拦截器可以检测到，可以在请求发出去之前做一些事情
axios.interceptors.request.use((config) => {//config:配置对象，对象里面有一个属性很重要，headers请求头console.log('请求拦截器执行', config);if(Date.now() % 2 === 0) {config.headers.token = 'zzy'; //模拟修改请求头}nprogress.start(); //进度条开始return config;  //检查完再把东西还给人家
});

2.响应拦截器

是得到响应之后执行的一组回调函数，若请求成功，对成功的数据（成功Promise的结果值）进行处理；若请求失败，对失败进行统一的操作。

//响应拦截器
axios.interceptors.response.use((res) => {console.log('响应拦截器成功的回调执行了，响应对象是：',res);//成功的回调函数，服务器响应数据回来以后，响应拦截器可以检测到，可以做一些事情nprogress.done(); //进度条结束return res.data;//检查完把东西还给人家并加工一下，直接把.data给Promise结果值},(error) => {console.log('响应拦截器失败的回调执行了');alert(error);//响应失败的回调函数，返回值和then的规则一样//若返回非Promise则走成功的回调，返回Promise则根据状态决定return Promise.reject(error);});

当请求结束后，如果请求成功，就会走第一个回调，然后再走then中成功的回调，所以这里的返回值就是Promise成功的值；如果请求失败，会先走第二个失败的回调，然后根据返回值（非Promise还是Promise）决定是走then中成功的回调还是失败的回调

axios.get('http://www.zzy.com').then(res => {console.log('请求成功'，res);
}, err => {console.log('请求失败', err);
}

一般来说，我们都会省略then的失败回调，所有的错误都在响应拦截器中捕获，做法就是在响应拦截器失败的回调中进行错误提示，并返回一个pending状态的Promise，这样的话我们使用async/await就不用包try-catch了，then也就不用指定失败的回调了。

axios.interceptors.response.use((res) => {console.log('响应拦截器成功的回调执行了，响应对象是：',res);//成功的回调函数，服务器响应数据回来以后，响应拦截器可以检测到，可以做一些事情nprogress.done(); //进度条结束return res.data;//检查完把东西还给人家并加工一下，直接把.data给出去},(error) => {console.log('响应拦截器失败的回调执行了');alert(error);//响应失败的回调函数，返回值和then的规则一样//若返回非Promise则走成功的回调，返回Promise则根据状态决定return new Promise(()=>{});});......
const reqData = async () => {//这样就不用捕获异常了，因为异常都在拦截器中捕获了。const result = await axios.get('http://www.zzy.com');
}

9.取消请求

加个cancelToken的这玩意儿就能取消发送中的请求；取消请求后会走失败的回调（或拦截器的失败回调）

let cancel;
发请求的按钮.onclick = () => {if(cancel) calcel('取消了'); //用户反复点击，只发送最后一次请求axios({url: 'www.zzy.com',cancelToken: new CancelToken(c => {cancel = c;  //c是一个函数，调用c就会取消请求})}).then(res => {console.log('成功',res)}, err => {if(isCancel(err)) {console.log('用户取消了请求',err.message);}else {console.log('请求失败',err);}});
}关闭请求的按钮.onclick = () => {cancel();
}

取消请求放拦截器里：

let cancel;
axios.interceptors.request.use(config => {if(cancel) cancel('取消了');config.cancelToken = new CancelToken(c => {cancel = c;})return config;
});axios.interceptors.response.use(res => {return res.data;
}, err => {if(isCancel(err)) {console.log('用户取消了请求，原因是',err.message);} else {console.log('请求失败',err);}return new Promise(() => {});
})发请求的按钮.onclick = async() => {let result = await axios.get('www.zzy.com');console.log(result);
}

10.源码分析

留个坑，先去复习项目，学算法去了~