Install 'winston' 0.6.2, require it, then clean all module cache, install 'winston' 0.7.2 and require it. It will fail because 'winston' 0.6.x uses 'async' 0.1 whereas 'winston' 0.7.x uses 'async' 0.2, which has changed its main file. Since the main file name is kept in cache in the variable packageMainCache (in module.js), the module will not b…

node_cache_test.js

var npm = require('npm');

npm.load({}, function (er) {
  if (er) console.log(er)
  npm.commands.install(["[email protected]"], function (er, data) {
    if (er) {
      console.log("npm install failed: " + er);
    }
    else {
      var winston = require('winston');
      console.log("Winston version: " + winston.version);
      upgradeWinstonVersion();
    }
  });
  npm.on("log", function (message) { console.log(message) });
});


function cleanModuleCache(moduleName) {
  var mod = require.resolve(moduleName);
  if (mod && ((mod = require.cache[mod]) !== undefined)) {
    (function run(mod) {
      mod.children.forEach(function (child) {
        run(child);
      });
      delete require.cache[mod.id];
    })(mod);
  }

  Object.keys(module.constructor._pathCache).forEach(function(cacheKey) {
    if (cacheKey.indexOf(moduleName) > 0) {
      delete module.constructor._pathCache[cacheKey];
    }
  });
};

function upgradeWinstonVersion() {
  cleanModuleCache('winston');

  npm.commands.install(["[email protected]"], function (er, data) {
    if (er) {
      console.log("npm install failed: " + er);
    }
    else {
      var winston = require('winston');
      console.log("Winston version: " + winston.version);
    }
  });
}

It works indeed! But I think will look at other possibilities for what I wanted to achieve, and I will see if the issue get reopened. Thanks for your investigation!