从全局目录加载
如果 NODE_PATH 环境变量设置为以冒号分隔的绝对路径列表，则 Node.js 将在这些路径中搜索模块（如果它们在其他地方找不到）。
在 Windows 上，NODE_PATH 由分号 (;) 而不是冒号分隔。
在定义当前的模块解析算法之前，NODE_PATH 最初是为了支持从不同路径加载模块而创建的。
NODE_PATH 仍然受支持，但现在 Node.js 生态系统已经确定了用于定位依赖模块的约定，因此不太必要。
有时，当不知道必须设置 NODE_PATH 时，依赖 NODE_PATH 的部署会表现出意外的行为。
有时，模块的依赖项会发生变化，导致在搜索 NODE_PATH 时加载不同的版本（甚至不同的模块）。
此外，Node.js 将在以下 GLOBAL_FOLDERS 列表中搜索：
- 1:
$HOME/.node_modules - 2:
$HOME/.node_libraries - 3:
$PREFIX/lib/node
其中 $HOME 是用户的主目录，$PREFIX 是 Node.js 配置的 node_prefix。
这些主要是出于历史原因。
强烈建议将依赖项放在本地 node_modules 文件夹中。
这些将加载得更快，更可靠。
If the NODE_PATH environment variable is set to a colon-delimited list
of absolute paths, then Node.js will search those paths for modules if they
are not found elsewhere.
On Windows, NODE_PATH is delimited by semicolons (;) instead of colons.
NODE_PATH was originally created to support loading modules from
varying paths before the current module resolution algorithm was defined.
NODE_PATH is still supported, but is less necessary now that the Node.js
ecosystem has settled on a convention for locating dependent modules.
Sometimes deployments that rely on NODE_PATH show surprising behavior
when people are unaware that NODE_PATH must be set. Sometimes a
module's dependencies change, causing a different version (or even a
different module) to be loaded as the NODE_PATH is searched.
Additionally, Node.js will search in the following list of GLOBAL_FOLDERS:
- 1:
$HOME/.node_modules - 2:
$HOME/.node_libraries - 3:
$PREFIX/lib/node
Where $HOME is the user's home directory, and $PREFIX is the Node.js
configured node_prefix.
These are mostly for historic reasons.
It is strongly encouraged to place dependencies in the local node_modules
folder. These will be loaded faster, and more reliably.