ERROR  Error: The project seems to require yarn but it's not installed.
Error: The project seems to require yarn but it's not installed.
    at checkYarn (E:\VUE_PROJECT\game-vuetify\node_modules\@vue\cli-shared-utils\lib\env.js:46:43)
    at exports.hasProjectYarn (E:\VUE_PROJECT\game-vuetify\node_modules\@vue\cli-shared-utils\lib\env.js:42:10)
    at E:\VUE_PROJECT\game-vuetify\node_modules\@vue\cli-service\lib\commands\serve.js:314:34
    at Hook.eval [as callAsync] (eval at create (E:\VUE_PROJECT\game-vuetify\node_modules\tapable\lib\HookCodeFactory.js:33:10), <anonymous>:44:1)
    at Hook.CALL_ASYNC_DELEGATE [as _callAsync] (E:\VUE_PROJECT\game-vuetify\node_modules\tapable\lib\Hook.js:18:14)
    at Watching._done (E:\VUE_PROJECT\game-vuetify\node_modules\webpack\lib\Watching.js:287:28)
    at E:\VUE_PROJECT\game-vuetify\node_modules\webpack\lib\Watching.js:209:21
    at Compiler.emitRecords (E:\VUE_PROJECT\game-vuetify\node_modules\webpack\lib\Compiler.js:906:5)
    at E:\VUE_PROJECT\game-vuetify\node_modules\webpack\lib\Watching.js:187:22
    at E:\VUE_PROJECT\game-vuetify\node_modules\webpack\lib\Compiler.js:872:14
    at Hook.eval [as callAsync] (eval at create (E:\VUE_PROJECT\game-vuetify\node_modules\tapable\lib\HookCodeFactory.js:33:10), <anonymous>:12:1)
    at Hook.CALL_ASYNC_DELEGATE [as _callAsync] (E:\VUE_PROJECT\game-vuetify\node_modules\tapable\lib\Hook.js:18:14)
    at E:\VUE_PROJECT\game-vuetify\node_modules\webpack\lib\Compiler.js:869:27
    at E:\VUE_PROJECT\game-vuetify\node_modules\neo-async\async.js:2818:7
    at done (E:\VUE_PROJECT\game-vuetify\node_modules\neo-async\async.js:3522:9)
    at Hook.eval [as callAsync] (eval at create (E:\VUE_PROJECT\game-vuetify\node_modules\tapable\lib\HookCodeFactory.js:33:10), <anonymous>:6:1)

只需要把yarn.lock在该项目删除

然后全局安装就好了

npm install -g yarn