场景：使用create-react-app创建项目，由于前后分离开发，本地起一个服务http://localhost:3000。所以当使用自带fetch去请求API的时候就存在同源策略跨域问题，今天分享一个跨域调试小技巧，无需服务端配合。
方法一：
安装谷歌浏览器跨域插件：Allow-Control-Allow-Origin
注意：fetch请求中配置不可填写credentials: "include"
方法二：
通过proxy解决跨域问题，可以直接在package.json下配置，具体如下：
"proxy": "http://api.xxxx.com"
满足可以调用不同域下的API的需求，代码如下：
//package.json中加入
"proxy": {
"/api/RoomApi": {
"target": "http://api.xxxx.com",
"changeOrigin":true
},
"/api/v1":{
"target":"http://api.xxxx.com",
"changeOrigin":true
}
}
注意：第二种方法fetch在请求的时候要使用相对路径url，即：url='/master/login'。不可使用全路径：即：'http://api.xxxx.com/master/login'
我们在实际开发中，打包后上传到同域名路径就ok了，不需要设置webpack代理的，这时候我们在打包的时候就需要在package.json配置中关闭刚才设置的proxy，挺麻烦的，难免打包的时候忘记屏蔽掉。解决方法：
1.你也可以使用 create-react-app 提供的 yarn run eject 命令将所有内建的配置暴露出来
2.修改webpackDevServer.config.js文件添加
```注意：yarn run eject可能导致项目跑不起来，这时候执行yarn 或者 npm install即可 ```
(process.env.NODE_ENV === 'development') && (proxy = {
"/": {
"target": "http://api.xxxx.com",
"changeOrigin": true
}
});
webpackDevServer.config.js完整代码：
'use strict';
const errorOverlayMiddleware = require('react-dev-utils/errorOverlayMiddleware');
const noopServiceWorkerMiddleware = require('react-dev-utils/noopServiceWorkerMiddleware');
const ignoredFiles = require('react-dev-utils/ignoredFiles');
const config = require('./webpack.config.dev');
const paths = require('./paths');
const protocol = process.env.HTTPS === 'true' ? 'https' : 'http';
const host = process.env.HOST || '0.0.0.0';
module.exports = function(proxy, allowedHost) {
(process.env.NODE_ENV === 'development') && (proxy = {
"/": {
"target": "https://echo-dev.skyplan.online",
"changeOrigin": true
}
});
return {
// WebpackDevServer 2.4.3 introduced a security fix that prevents remote
// websites from potentially accessing local content through DNS rebinding:
// https://github.com/webpack/webpack-dev-server/issues/887
// https://medium.com/webpack/webpack-dev-server-middleware-security-issues-1489d950874a
// However, it made several existing use cases such as development in cloud
// environment or subdomains in development significantly more complicated:
// https://github.com/facebookincubator/create-react-app/issues/2271
// https://github.com/facebookincubator/create-react-app/issues/2233
// While we're investigating better solutions, for now we will take a
// compromise. Since our WDS configuration only serves files in the `public`
// folder we won't consider accessing them a vulnerability. However, if you
// use the `proxy` feature, it gets more dangerous because it can expose
// remote code execution vulnerabilities in backends like Django and Rails.
// So we will disable the host check normally, but enable it if you have
// specified the `proxy` setting. Finally, we let you override it if you
// really know what you're doing with a special environment variable.
disableHostCheck:
!proxy || process.env.DANGEROUSLY_DISABLE_HOST_CHECK === 'true',
// Enable gzip compression of generated files.
compress: true,
// Silence WebpackDevServer's own logs since they're generally not useful.
// It will still show compile warnings and errors with this setting.
clientLogLevel: 'none',
// By default WebpackDevServer serves physical files from current directory
// in addition to all the virtual build products that it serves from memory.
// This is confusing because those files won’t automatically be available in
// production build folder unless we copy them. However, copying the whole
// project directory is dangerous because we may expose sensitive files.
// Instead, we establish a convention that only files in `public` directory
// get served. Our build script will copy `public` into the `build` folder.
// In `index.html`, you can get URL of `public` folder with %PUBLIC_URL%:
// <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
// In JavaScript code, you can access it with `process.env.PUBLIC_URL`.
// Note that we only recommend to use `public` folder as an escape hatch
// for files like `favicon.ico`, `manifest.json`, and libraries that are
// for some reason broken when imported through Webpack. If you just want to
// use an image, put it in `src` and `import` it from JavaScript instead.
contentBase: paths.appPublic,
// By default files from `contentBase` will not trigger a page reload.
watchContentBase: true,
// Enable hot reloading server. It will provide /sockjs-node/ endpoint
// for the WebpackDevServer client so it can learn when the files were
// updated. The WebpackDevServer client is included as an entry point
// in the Webpack development configuration. Note that only changes
// to CSS are currently hot reloaded. JS changes will refresh the browser.
hot: true,
// It is important to tell WebpackDevServer to use the same "root" path
// as we specified in the config. In development, we always serve from /.
publicPath: config.output.publicPath,
// WebpackDevServer is noisy by default so we emit custom message instead
// by listening to the compiler events with `compiler.plugin` calls above.
quiet: true,
// Reportedly, this avoids CPU overload on some systems.
// https://github.com/facebookincubator/create-react-app/issues/293
// src/node_modules is not ignored to support absolute imports
// https://github.com/facebookincubator/create-react-app/issues/1065
watchOptions: {
ignored: ignoredFiles(paths.appSrc),
},
// Enable HTTPS if the HTTPS environment variable is set to 'true'
https: protocol === 'https',
host: host,
overlay: false,
historyApiFallback: {
// Paths with dots should still use the history fallback.
// See https://github.com/facebookincubator/create-react-app/issues/387.
disableDotRule: true,
},
public: allowedHost,
proxy,
before(app) {
// This lets us open files from the runtime error overlay.
app.use(errorOverlayMiddleware());
// This service worker file is effectively a 'no-op' that will reset any
// previous service worker registered for the same host:port combination.
// We do this in development to avoid hitting the production cache if
// it used the same host and port.
// https://github.com/facebookincubator/create-react-app/issues/2272#issuecomment-302832432
app.use(noopServiceWorkerMiddleware());
},
};
};
