关于node.js的模块查找顺序（require.resolve()）
前几天社团群里有人问了阿里秋季前端笔试的一道题，想起来以前在官方文档看到过查找模块的算法，干脆自己写一写……
官方的require.resolve实现在这里. 因为我只是想看看查找过程，所以就直接把会被找的路径console.log出来看看而已。代码放在了我的github gist上：https://gist.github.com/joyeec9h3/74262a250b3e880c7fd4
结果如下
--------------------------------------- check /home/somebody/node_modules/othermodule check /home/somebody/node_modules/othermodule.js check /home/somebody/node_modules/othermodule.json check /home/somebody/node_modules/othermodule.node --------------------------------------- if /home/somebody/node_modules/othermodule/package.json exists check /home/somebody/node_modules/othermodule/package.json[main] --------------------------------------- if /home/somebody/node_modules/othermodule/index.js exists check /home/somebody/node_modules/othermodule/index.js --------------------------------------- if /home/somebody/node_modules/othermodule/index.node exists check /home/somebody/node_modules/othermodule/index.node --------------------------------------- check /home/node_modules/othermodule check /home/node_modules/othermodule.js check /home/node_modules/othermodule.json check /home/node_modules/othermodule.node --------------------------------------- if /home/node_modules/othermodule/package.json exists check /home/node_modules/othermodule/package.json[main] --------------------------------------- if /home/node_modules/othermodule/index.js exists check /home/node_modules/othermodule/index.js --------------------------------------- if /home/node_modules/othermodule/index.node exists check /home/node_modules/othermodule/index.node --------------------------------------- check /node_modules/othermodule check /node_modules/othermodule.js check /node_modules/othermodule.json check /node_modules/othermodule.node --------------------------------------- if /node_modules/othermodule/package.json exists check /node_modules/othermodule/package.json[main] --------------------------------------- if /node_modules/othermodule/index.js exists check /node_modules/othermodule/index.js --------------------------------------- if /node_modules/othermodule/index.node exists check /node_modules/othermodule/index.node --------------------------------------- for each $PATH in $NODE_PATH --------------------------------------- if $PATH/package.json exists check $PATH/package.json[main] --------------------------------------- if $PATH/index.js exists check $PATH/index.js --------------------------------------- if $PATH/index.node exists check $PATH/index.node --------------------------------------- if $HOME/.node_modules/package.json exists check $HOME/.node_modules/package.json[main] --------------------------------------- if $HOME/.node_modules/index.js exists check $HOME/.node_modules/index.js --------------------------------------- if $HOME/.node_modules/index.node exists check $HOME/.node_modules/index.node --------------------------------------- if $HOME/.node_libraries/package.json exists check $HOME/.node_libraries/package.json[main] --------------------------------------- if $HOME/.node_libraries/index.js exists check $HOME/.node_libraries/index.js --------------------------------------- if $HOME/.node_libraries/index.node exists check $HOME/.node_libraries/index.node --------------------------------------- if $PREFIX/lib/node/package.json exists check $PREFIX/lib/node/package.json[main] --------------------------------------- if $PREFIX/lib/node/index.js exists check $PREFIX/lib/node/index.js --------------------------------------- if $PREFIX/lib/node/index.node exists check $PREFIX/lib/node/index.node
简单来说，如果是require('x')这样开头不是相对or绝对地址符号，尾巴也没说是.js或者.json的，就当做模块来找。先找是不是core module，然后一级一级向上看node_modules文件夹，每一级的node_modules先看里面是否有basename为所找的文件，再看是否有模块名文件夹下package.json的main标明的文件，然后不死心地看看模块名文件夹下有没有index.js和index.node。最后找不到的话，还要搜一遍全局环境，比如$HOME/.node_modules/什么的。
