引子
阮一峰一则教程中， 将应用放置在 npm 模块安装目录同等级的目录（https://github.com/ruanyf/webpack-demos）下。
但是应用目录文件中， 引用标准库的使用方法没有变化
https://github.com/ruanyf/webpack-demos/blob/master/demo15/index.js
如下代码
import React from ‘react‘;import { render } from ‘react-dom‘;import { BrowserRouter, Switch, Route, Link } from ‘react-router-dom‘;NodeJS的寻址规则是怎么样的呢？
尽管这个是前端的代码， 但是我们知道实际上引用模块，并打包的动作， 是交给 webpack来的做得。
但是模块的寻址规则， 则是哪找NodeJS的文件寻址规则， 没有改变，而是打包后， 变成前端可执行的集成代码。
寻址规则
https://nodejs.org/api/modules.html#modules_accessing_the_main_module
require(X) from module at path Y1. If X is a core module, ??a. return the core module ??b. STOP2. If X begins with ‘/‘ ??a. set Y to be the filesystem root3. If X begins with ‘./‘ or ‘/‘ or ‘../‘ ??a. LOAD_AS_FILE(Y + X) ??b. LOAD_AS_DIRECTORY(Y + X)4. LOAD_NODE_MODULES(X, dirname(Y))5. THROW "not found"LOAD_AS_FILE(X)1. If X is a file, load X as JavaScript text. ?STOP2. If X.js is a file, load X.js as JavaScript text. ?STOP3. If X.json is a file, parse X.json to a JavaScript Object. ?STOP4. If X.node is a file, load X.node as binary addon. ?STOPLOAD_INDEX(X)1. If X/index.js is a file, load X/index.js as JavaScript text. ?STOP2. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP3. If X/index.node is a file, load X/index.node as binary addon. ?STOPLOAD_AS_DIRECTORY(X)1. If X/package.json is a file, ??a. Parse X/package.json, and look for "main" field. ??b. let M = X + (json main field) ??c. LOAD_AS_FILE(M) ??d. LOAD_INDEX(M)2. LOAD_INDEX(X)LOAD_NODE_MODULES(X, START)1. let DIRS = NODE_MODULES_PATHS(START)2. for each DIR in DIRS: ??a. LOAD_AS_FILE(DIR/X) ??b. LOAD_AS_DIRECTORY(DIR/X)NODE_MODULES_PATHS(START)1. let PARTS = path split(START)2. let I = count of PARTS - 13. let DIRS = [GLOBAL_FOLDERS]4. while I >= 0, ??a. if PARTS[I] = "node_modules" CONTINUE ??b. DIR = path join(PARTS[0 .. I] + "node_modules") ??c. DIRS = DIRS + DIR ??d. let I = I - 15. return DIRS
nodeJS模块寻址规则
原文地址：https://www.cnblogs.com/lightsong/p/10540419.html