两种方法选其一即可

一、后端koa设置中间件

app.use(async (ctx, next)=> {ctx.set('Access-Control-Allow-Origin', '*');ctx.set('Access-Control-Allow-Headers', 'Content-Type, Content-Length, Authorization, Accept, X-Requested-With , yourHeaderFeild');ctx.set('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');if (ctx.method == 'OPTIONS') {ctx.body = 200; } else {await next();}})

二、前端

1.vite.config.ts文件配置proxy代理

import { defineConfig } from 'vite'
import AutoImport from 'unplugin-auto-import/vite'
import Components from 'unplugin-vue-components/vite'
import { ElementPlusResolver } from 'unplugin-vue-components/resolvers'
import path from 'path'
import vue from '@vitejs/plugin-vue'// https://vitejs.dev/config/
export default defineConfig({plugins: [vue(),AutoImport({resolvers: [ElementPlusResolver()],}),Components({resolvers: [ElementPlusResolver()],}),],resolve: {alias: {'@': path.resolve(__dirname, './src')},},css: {preprocessorOptions: {scss: {additionalData: `@use "@/style/global.scss" as *;`,}}},server:{proxy:{"/api":{target:"http://localhost:3000/",changeOrigin: true,rewrite: (path) => path.replace(/^\/api/, '')}}}
})

2.axios配置文件

import axios from 'axios';const http=axios.create({baseURL:'/api',timeout: 1000
})export default http;

3.在main.ts文件中引入axios

import { createApp } from 'vue'
import './style.scss'
import App from './App.vue'
import ElementPlus from 'element-plus'
import 'element-plus/dist/index.css'
import {router} from './router/index.ts'import axios from 'axios'createApp(App).use(ElementPlus).use(router).mount('#app')
createApp(App).config.globalProperties.$axios=axios

三、使用

import http from '@/plugins/axios'
import {onMounted,ref} from 'vue';const getData = async () => {http.get('/products').then(res=>{console.log('test.res');})
}