A simplified version of the require.resovle() from node.js

resolve.js

var path = require('path');

// require(X) from module at path Y
function resolve(x, y) {
   // 1. If X is a core module,
   //    a. return the core module
   //    b. STOP
   if (isCoreModule(x)) {
      console.log(x + " is a core module");
   }

   // 2. If X begins with './' or '/' or '../'
   //    a. LOAD_AS_FILE(Y + X)
   //    b. LOAD_AS_DIRECTORY(Y + X)
   var pathPrefixes = ['./', '/', '../'];
   pathPrefixes.forEach(function(prefix) {
      if (x.indexOf(prefix) == 0) {
         loadAsFile(y + x);
         loadAsDirectory(y + x);
      }
   });

   // 3. LOAD_NODE_MODULES(X, dirname(Y))
   loadNodeModules(x, path.dirname(y));

   // addition: load from global env
   console.log('---------------------------------------');
   console.log('\nfor each $PATH in $NODE_PATH\n');
   loadAsDirectory('$PATH');

   loadAsDirectory('$HOME/.node_modules');
   loadAsDirectory('$HOME/.node_libraries');
   loadAsDirectory('$PREFIX/lib/node');
   // 4. THROW "not found"  
}

// LOAD_AS_FILE(X)
function loadAsFile(x) {
   console.log('---------------------------------------');
   // 1. If X is a file, load X as JavaScript text.  STOP
   console.log("\tcheck " + x);
   // 2. If X.js is a file, load X.js as JavaScript text.  STOP
   console.log("\tcheck " + x + ".js");
   // 3. If X.json is a file, parse X.json to a JavaScript Object.  STOP
   console.log("\tcheck " + x + ".json");
   // 4. If X.node is a file, load X.node as binary addon.  STOP
   console.log("\tcheck " + x + ".node");
}

// LOAD_AS_DIRECTORY(X)
function loadAsDirectory(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)
   console.log('---------------------------------------');
   console.log("if " + x + "/package.json exists");
   console.log("\tcheck " + x + "/package.json[main]");

   // 2. If X/index.js is a file, load X/index.js as JavaScript text.  STOP
   console.log('---------------------------------------');
   console.log("if " + x + "/index.js exists");
   console.log("\tcheck " + x + "/index.js");

   // 3. If X/index.node is a file, load X/index.node as binary addon.  STOP
   console.log('---------------------------------------');
   console.log("if " + x + "/index.node exists");
   console.log("\tcheck " + x + "/index.node");
}

// LOAD_NODE_MODULES(X, START)
function loadNodeModules(x, start) {
   // 1. let DIRS=NODE_MODULES_PATHS(START)
   var dirs = nodeModulesPaths(start);

   // 2. for each DIR in DIRS:
   dirs.forEach(function(dir) {
      //    a. LOAD_AS_FILE(DIR/X)
      loadAsFile(dir + '/' + x);
      //    b. LOAD_AS_DIRECTORY(DIR/X)
      loadAsDirectory(dir + '/' + x);
   });
}

// NODE_MODULES_PATHS(START)
function nodeModulesPaths(start) {
   // 1. let PARTS = path split(START)
   var parts = start.split('/');
   // 2. let ROOT = index of first instance of "node_modules" in PARTS, or 0
   var root = parts[0];
   // 3. let I = count of PARTS - 1
   var i = parts.length - 1
      // 4. let DIRS = []
   dirs = []
   // 5. while I > ROOT,
   while (i >= 0) {
      //    a. if PARTS[I] = "node_modules" CONTINUE
      if (parts[i] == 'node_modules') {
         continue;
      }
      //    c. DIR = path join(PARTS[0 .. I] + "node_modules")
      var dirParts = parts.slice(0, i + 1);
      dirParts.push('node_modules');
      var dir = dirParts.join('/');

      //    b. DIRS = DIRS + DIR
      dirs.push(dir);

      //    c. let I = I - 1
      i -= 1;
   }
   // 6. return DIRS

   return dirs;
}

function isCoreModule(x) {
   var core = ["assert", "buffer", "child_process",
      "cluster", "console", "constants", "crypto",
      "dgram", "dns", "domain", "events", "freelist",
      "fs", "http", "https", "module", "net", "os", "path",
      "punycode", "querystring", "readline", "repl", "smalloc",
      "stream", "string_decoder", "sys", "timers", "tls", "tracing",
      "tty", "url", "util", "vm", "zlib"
   ];
   for (var i = 0; i < core.length; ++i) {
      if (x == core[i]) {
         return true;
      }
   }

   return false;
}

resolve('othermodule','/home/somebody/workspace/')