npm WARN checkPermissions Missing write access to /usr/local/lib/node_modules/webpack/node_modules/_schema-utils@1.0.0@schema-utils/node_modules/ajv
npm WARN checkPermissions Missing write access to /usr/local/lib/node_modules/webpack/node_modules/_schema-utils@1.0.0@schema-utils/node_modules/ajv-keywords
npm WARN checkPermissions Missing write access to /usr/local/lib/node_modules/webpack/node_modules/terser-webpack-plugin
npm WARN checkPermissions Missing write access to /usr/local/lib/node_modules/webpack/node_modules/watchpack
npm WARN checkPermissions Missing write access to /usr/local/lib/node_modules/webpack/node_modules/is-descriptor/node_modules
npm ERR! path /usr/local/lib/node_modules/webpack/node_modules/assert
npm ERR! code ENOENT
npm ERR! errno -2
npm ERR! syscall access
npm ERR! enoent ENOENT: no such file or directory, access '/usr/local/lib/node_modules/webpack/node_modules/assert'
npm ERR! enoent This is related to npm not being able to find a file.
npm ERR! enoent
npm ERR! A complete log of this run can be found in:
npm ERR! /Users/zhouqiang/.npm/_logs/2018-12-11T11_57_35_887Z-debug.log
出现这种情况我建议你还是重新安装node吧
可以通过命令查看一下npm配置
npm list -g