Question

Quick question, but one I surprisingly couldn’t find the answer for with a bit of Googling… when I use the node interactive interpreter, I can type in the names of basically all core modules and see them output as objects onto the console… however, I understand that the core modules aren’t all included like this by default when running a .js file.

Can anyone clear this up for me? All help appreciated.

Answer 1

Starting in Node 0.8, repl.js defines a list of built-in libraries that will be automatically required when you type their name on the REPL:

exports._builtinLibs = ['assert', 'buffer', 'child_process', 'cluster',
  'crypto', 'dgram', 'dns', 'events', 'fs', 'http', 'https', 'net',
  'os', 'path', 'punycode', 'querystring', 'readline', 'repl',
  'string_decoder', 'tls', 'tty', 'url', 'util', 'vm', 'zlib'];

...

if (exports._builtinLibs.indexOf(cmd) !== -1) {
  var lib = require(cmd);
  if (cmd in self.context && lib !== self.context[cmd]) {
    self.outputStream.write('A different "' + cmd +
                            '" already exists globally\n');
  } else {
    self.context._ = self.context[cmd] = lib;
    self.outputStream.write(self.writer(lib) + '\n');
  }
  self.displayPrompt();
  return;
}

This is specifically a function of repl.js, and does not work at all in any way when writing your own Node.js programs; there, you must specifically require anything you want to use.