npm git ignore node_modules: ignores npm modules in the node_modules directory by consulting the devDependencies field in the package.json

ignore.js

#!/usr/bin/env node
var fs = require('fs');
var path = require('path');

var hasOwn = Object.prototype.hasOwnProperty;

// seaches recursively upwards to find the package.json
function load(start, name) {
  var exists, full;
  do {
    exists = fs.existsSync(full = path.join(start, name));
    start = path.dirname(start);
  } while (!exists && start !== path.dirname(start));
  if (!exists)
    throw new Error('cannot locate ' + name);
  var obj = require(full);
  if (!obj || typeof obj !== 'object')
    throw new TypeError('expected object');
  return {
    path: path.dirname(full),
    full: full,
    file: obj
  };
}

var obj = load(process.cwd(), 'package.json'), package = obj.file;
var ignore = package.devDependencies;
var gitignore = path.join(obj.path, '.gitignore');

if (!ignore || typeof ignore !== 'object')
  return console.warn('no development dependencies');

for (var key in ignore) {
  ignore['/node_modules/' + key] = ignore[key];
  delete ignore[key];
}

var lines;

if (!fs.existsSync(gitignore))
  lines = [];
else {
  lines = fs.readFileSync(gitignore, 'utf-8').split(/\r?\n/g);
  lines.forEach(function(line) {
    line = line && line.trim();
    if (line && hasOwn.call(ignore, line)) {
      delete ignore[line];
    }
  });
}

lines = lines.concat(Object.keys(ignore), ['']).join('\n');

if (~process.argv.indexOf('--print'))
  return console.log(lines);

fs.writeFileSync(gitignore, lines);