“npm config set prefix”在 macOS Mojave 中的用户拥有的目录上失败

我正在使用 Homebrew 在干净的 macOS Mojave 机器上安装节点。我正在尝试在用户拥有的目录中设置 npm 安装目录；该目录tools已存在并归用户所有：

npm config set prefix '/Users/giorgio/tools/npm_global'

这条消息失败了。有谁知道发生了什么事？

Error: EACCES: permission denied, mkdir '/tools'
TypeError: Cannot read property 'loaded' of undefined
    at exit (/usr/local/lib/node_modules/npm/lib/utils/error-handler.js:98:27)
    at errorHandler (/usr/local/lib/node_modules/npm/lib/utils/error-handler.js:216:3)
    at /usr/local/lib/node_modules/npm/bin/npm-cli.js:78:20
    at cb (/usr/local/lib/node_modules/npm/lib/npm.js:225:22)
    at /usr/local/lib/node_modules/npm/lib/npm.js:263:24
    at /usr/local/lib/node_modules/npm/lib/config/core.js:83:7
    at Array.forEach (<anonymous>)
    at /usr/local/lib/node_modules/npm/lib/config/core.js:82:13
    at f (/usr/local/lib/node_modules/npm/node_modules/once/once.js:25:25)
    at afterExtras (/usr/local/lib/node_modules/npm/lib/config/core.js:173:20)
/usr/local/lib/node_modules/npm/lib/utils/error-handler.js:98
  var doExit = npm.config.loaded ? npm.config.get('_exit') : true
                          ^

TypeError: Cannot read property 'loaded' of undefined
    at exit (/usr/local/lib/node_modules/npm/lib/utils/error-handler.js:98:27)
    at process.errorHandler (/usr/local/lib/node_modules/npm/lib/utils/error-handler.js:216:3)
    at process.emit (events.js:197:13)
    at process._fatalException (internal/process/execution.js:123:25)