npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: routerdemo@0.1.0
npm ERR! Found: vue@2.6.14
npm ERR! node_modules/vue
npm ERR! vue@"^2.6.14" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer vue@"^3.2.0" from vue-router@4.0.15
npm ERR! node_modules/vue-router
npm ERR! vue-router@"*" from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
npm ERR!
npm ERR! See D:\Node.js\node_cache\eresolve-report.txt for a full report.

npm ERR! A complete log of this run can be found in:

安装失败的原因是：我安装的是Choose a version of Vue.js that you want to start the project with 2.x ，vue2.x版本兼用不了最新的版本的router，即这条命令（npm install vue-router -S），它默认安装高版本，解决方法：npm i vue-router@3.5.2（router版本） -S，用低版本即可