node 加载逻辑

【node 加载逻辑】

　　

require(X) from module at path Y
. If X is a core module,
   a. return the core module
   b. STOP
. If X begins with './' or '/' or '../'
   a. LOAD_AS_FILE(Y + X)
   b. LOAD_AS_DIRECTORY(Y + X)
. LOAD_NODE_MODULES(X, dirname(Y))
. THROW "not found"

LOAD_AS_FILE(X)
. If X is a file, load X as JavaScript text.  STOP
. If X.js is a file, load X.js as JavaScript text.  STOP
. If X.json is a file, parse X.json to a JavaScript Object.  STOP
. If X.node is a file, load X.node as binary addon.  STOP

LOAD_AS_DIRECTORY(X)
. 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)
. If X/index.js is a file, load X/index.js as JavaScript text.  STOP
. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP
. If X/index.node is a file, load X/index.node as binary addon.  STOP

LOAD_NODE_MODULES(X, START)
. let DIRS=NODE_MODULES_PATHS(START)
. for each DIR in DIRS:
   a. LOAD_AS_FILE(DIR/X)
   b. LOAD_AS_DIRECTORY(DIR/X)

NODE_MODULES_PATHS(START)
. let PARTS = path split(START)
. let I = count of PARTS -
. let DIRS = []
. while I >= ,
   a. if PARTS[I] = "node_modules" CONTINUE
   b. DIR = path join(PARTS[ .. I] + "node_modules")
   c. DIRS = DIRS + DIR
   d. let I = I -
. return DIRS

参考：https://nodejs.org/api/modules.html