builder-shorthands.js

var shorthands = require('./shorthands');

/**
 * Mixin shorthands.
 */

for (var key in shorthands) Builder.prototype[key] = shorthands[key];

plugins-exports.js

/**
 * Expose `exprts`.
 */
 
module.exports = exprts;

/**
 * Exports plugin example.
 *
 * @param {String} type
 */

function exprts (type) {
  return function (build, fn) {
    setImmediate(fn);
    build.each(type, function (file) {
      if (!file.contents) return;
      file.contents = 'module.exports = ' + file.contents;
    });
  });
};

plugins-string.js

var str2js = require('string-to-js');

/**
 * Expose `string`.
 */
 
module.exports = string;

/**
 * String plugin example.
 *
 * @param {String} type
 */

function string (type) {
  return function (build, fn) {
    setImmediate(fn);
    build.each(type, function (file) {
      if (!file.contents) return;
      file.contents = str2js(file.contents);
    });
  });
}

shorthands.js

var concat = require('./plugins/concat');
var copy = require('./plugins/copy');
var string = require('./plugins/string');
var exps = require('./plugins/exports');

/**
 * Build scripts shorthand.
 *
 * @param {Function} fn
 */

exports.scripts = function (fn) {
  this
    .use(concat('scripts'))
    .build(fn);
};

/**
 * Build styles shorthand.
 *
 * @param {Function} fn
 */

exports.styles = function (fn) {
  this
    .use(concat('styles'))
    .build(fn);
};

/**
 * Build templates shorthand.
 *
 * @param {Function} fn
 */

exports.templates = function (fn) {
  this
    .use(string('templates'))
    .use(concat('templates'))
    .build(fn);
};

/**
 * Build json shorthand.
 *
 * @param {Function} fn
 */

exports.json = function (fn) {
  this
    .use(exps('json'))
    .use(concat('json'))
    .build(fn);
};

/**
 * Build images shorthand.
 *
 * @param {Function} fn
 */

exports.images = function (fn) {
  this
    .use(copy('images'))
    .build(fn);
};

/**
 * Build fonts shorthand.
 *
 * @param {Function} fn
 */

exports.fonts = function (fn) {
  this
    .use(copy('fonts'))
    .build(fn);
};

i'm not totally sure about what's going on here, but why not something like:

builder.use('fonts', copy)
builder.use('scripts', concat)
builder.use('templates', string, concat)