Grunt task to error out if files are missing

Gruntfile.js

var _ = require('lodash');

module.exports = function(grunt) {

  grunt.registerMultiTask('check', 'Check for the existence of files', function() {
    var filesMissing = false;
    
    // Flatten the nested source arrays -- I used _.flatten, there are other methods
    _.flatten( this.data ).forEach(function( filepath ) {
      if ( ! grunt.file.exists(filepath) ) {
        filesMissing = true;
        grunt.log.error( 'Missing File: ' + filepath );
      }
    });

    // Return false to error out:
    // remove this if you want to continue even if files are missing
    if ( filesMissing ) {
      return false;
    }
  });

  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    check: {
      source: [
        '<%= pkg.gruntConfig.js.dist.default %>',
        '<%= pkg.gruntConfig.js.dev.default %>'
      ]
    },
    // OR
    check: [
      '<%= pkg.gruntConfig.js.dist.default %>',
      '<%= pkg.gruntConfig.js.dev.default %>'
    ],
    // ....
  });
};