index.js

module.exports = worker

var prelude = require('./prelude')
  , path = require('path')
  , cache = {}
  , make_blob
  , make_url

switch(true) {
  case typeof Blob !== 'undefined':
    make_blob = function(data) {
      return new Blob([data], {'type': 'text/javascript'})
    }
    break
  case typeof BlobBuilder !== 'undefined':
    make_blob = builder(BlobBuilder)
    break
  case typeof MSBlobBuilder !== 'undefined':
    make_blob = builder(MSBlobBuidler)
    break
  case typeof MozBlobBuilder !== 'undefined':
    make_blob = builder(MozBlobBuidler)
    break
  case typeof WebKitBlobBuilder !== 'undefined':
    make_blob = builder(WebKitBlobBuilder)
    break
}

switch(true) {
  case typeof URL !== 'undefined' && !!URL.createObjectURL:
    make_url = urler(URL)
    break
  case typeof webkitURL !== 'undefined' && !!webkitURL.createObjectURL:
    make_url = urler(webkitURL)
    break
  case typeof msURL !== 'undefined' && !!msURL.createObjectURL:
    make_url = urler(msURL)
    break
  case typeof MozURL !== 'undefined' && !!MozURL.createObjectURL:
    make_url = urler(MozURL)
    break
}

function worker(fn, dir) {
  if(typeof fn !== 'string') {
    if(cache[dir] && cache[dir][0] === fn) {
      return new Worker(cache[dir][1])
    }
  }

  fn = fn+''

  var src = make_src(fn, dir)
    , blob = make_blob(src)
    , url = make_url(blob)
    , worker = new Worker(url)

  cache[dir] = [fn, url]

  return worker
}

function builder(type) {
  return function(data) {
    var bb = new type
    bb.append(data)
    return bb.getBlob('text/javascript')
  }
}

function urler(type) {
  return function(blob) {
    return type.createObjectURL(blob)
  }
}

function make_src(fn, dir) {
  var src = [''+prelude.replace('$extensions', '{}')]
    , entry = JSON.stringify(path.join(dir, 'worker.js')) 

  for(var key in require.modules) {
    src.push('require.define('+JSON.stringify(key)+', '+require.modules[key].source+');')
  }

  src.push('require.define('+entry+', '+
  'function(require,module,exports,__dirname,__filename,process,global) { !'+fn+'() });'+
  'require('+entry+');')

  return src.join('')
}

prelude.js

module.exports="var require = function (file, cwd) {\n    var resolved = require.resolve(file, cwd || '/');\n    var mod = require.modules[resolved];\n    if (!mod) throw new Error(\n        'Failed to resolve module ' + file + ', tried ' + resolved\n    );\n    var cached = require.cache[resolved];\n    var res = cached? cached.exports : mod();\n    return res;\n};\n\nrequire.paths = [];\nrequire.modules = {};\nrequire.cache = {};\nrequire.extensions = $extensions;\n\nrequire._core = {\n    'assert': true,\n    'events': true,\n    'fs': true,\n    'path': true,\n    'vm': true\n};\n\nrequire.resolve = (function () {\n    return function (x, cwd) {\n        if (!cwd) cwd = '/';\n        \n        if (require._core[x]) return x;\n        var path = require.modules.path();\n        cwd = path.resolve('/', cwd);\n        var y = cwd || '/';\n        \n        if (x.match(/^(?:\\.\\.?\\/|\\/)/)) {\n            var m = loadAsFileSync(path.resolve(y, x))\n                || loadAsDirectorySync(path.resolve(y, x));\n            if (m) return m;\n        }\n        \n        var n = loadNodeModulesSync(x, y);\n        if (n) return n;\n        \n        throw new Error(\"Cannot find module '\" + x + \"'\");\n        \n        function loadAsFileSync (x) {\n            x = path.normalize(x);\n            if (require.modules[x]) {\n                return x;\n            }\n            \n            for (var i = 0; i < require.extensions.length; i++) {\n                var ext = require.extensions[i];\n                if (require.modules[x + ext]) return x + ext;\n            }\n        }\n        \n        function loadAsDirectorySync (x) {\n            x = x.replace(/\\/+$/, '');\n            var pkgfile = path.normalize(x + '/package.json');\n            if (require.modules[pkgfile]) {\n                var pkg = require.modules[pkgfile]();\n                var b = pkg.browserify;\n                if (typeof b === 'object' && b.main) {\n                    var m = loadAsFileSync(path.resolve(x, b.main));\n                    if (m) return m;\n                }\n                else if (typeof b === 'string') {\n                    var m = loadAsFileSync(path.resolve(x, b));\n                    if (m) return m;\n                }\n                else if (pkg.main) {\n                    var m = loadAsFileSync(path.resolve(x, pkg.main));\n                    if (m) return m;\n                }\n            }\n            \n            return loadAsFileSync(x + '/index');\n        }\n        \n        function loadNodeModulesSync (x, start) {\n            var dirs = nodeModulesPathsSync(start);\n            for (var i = 0; i < dirs.length; i++) {\n                var dir = dirs[i];\n                var m = loadAsFileSync(dir + '/' + x);\n                if (m) return m;\n                var n = loadAsDirectorySync(dir + '/' + x);\n                if (n) return n;\n            }\n            \n            var m = loadAsFileSync(x);\n            if (m) return m;\n        }\n        \n        function nodeModulesPathsSync (start) {\n            var parts;\n            if (start === '/') parts = [ '' ];\n            else parts = path.normalize(start).split('/');\n            \n            var dirs = [];\n            for (var i = parts.length - 1; i >= 0; i--) {\n                if (parts[i] === 'node_modules') continue;\n                var dir = parts.slice(0, i + 1).join('/') + '/node_modules';\n                dirs.push(dir);\n            }\n            \n            return dirs;\n        }\n    };\n})();\n\nrequire.alias = function (from, to) {\n    var path = require.modules.path();\n    var res = null;\n    try {\n        res = require.resolve(from + '/package.json', '/');\n    }\n    catch (err) {\n        res = require.resolve(from, '/');\n    }\n    var basedir = path.dirname(res);\n    \n    var keys = (Object.keys || function (obj) {\n        var res = [];\n        for (var key in obj) res.push(key);\n        return res;\n    })(require.modules);\n    \n    for (var i = 0; i < keys.length; i++) {\n        var key = keys[i];\n        if (key.slice(0, basedir.length + 1) === basedir + '/') {\n            var f = key.slice(basedir.length);\n            require.modules[to + f] = require.modules[basedir + f];\n        }\n        else if (key === basedir) {\n            require.modules[to] = require.modules[basedir];\n        }\n    }\n};\n\n(function () {\n    var process = {};\n    var global = typeof window !== 'undefined' ? window : {};\n    var definedProcess = false;\n    \n    require.define = function (filename, fn) {\n        if (!definedProcess && require.modules.__browserify_process) {\n            process = require.modules.__browserify_process();\n            definedProcess = true;\n        }\n        \n        var dirname = require._core[filename]\n            ? ''\n            : require.modules.path().dirname(filename)\n        ;\n        \n        var require_ = function (file) {\n            var requiredModule = require(file, dirname);\n            var cached = require.cache[require.resolve(file, dirname)];\n\n            if (cached && cached.parent === null) {\n                cached.parent = module_;\n            }\n\n            return requiredModule;\n        };\n        require_.resolve = function (name) {\n            return require.resolve(name, dirname);\n        };\n        require_.modules = require.modules;\n        require_.define = require.define;\n        require_.cache = require.cache;\n        var module_ = {\n            id : filename,\n            filename: filename,\n            exports : {},\n            loaded : false,\n            parent: null\n        };\n        \n        require.modules[filename] = function () {\n            require.cache[filename] = module_;\n            fn.call(\n                module_.exports,\n                require_,\n                module_,\n                module_.exports,\n                dirname,\n                filename,\n                process,\n                global\n            );\n            module_.loaded = true;\n            return module_.exports;\n        };\n    };\n})();\n"