factor browser-pack bundles into common shared bundles
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factor browser-pack bundles into a common bundle and entry-specific bundles

build status



var z = require('./z.js');
var w = require('./w.js');
console.log(z(5) * w(2));


var z = require('./z.js');
console.log(z(2) + 111);


module.exports = function (n) { return n * 111 }


module.exports = function (n) { return n * 50 }

Now run factor-bundle as a plugin (new in browserify 3.28.0):

browserify x.js y.js -p [ factor-bundle -o bundle/x.js -o bundle/y.js ] \
  -o bundle/common.js

or you can pipe module-deps json directly into the factor-bundle command:

$ module-deps x.js y.js | factor-bundle \
  x.js -o bundle/x.js \
  y.js -o bundle/y.js \
  > bundle/common.js

or factor out an existing bundle already compiled by browserify:

$ browserify x.js y.js > bundle.js
$ browser-unpack < bundle.js | factor-bundle \
  x.js -o bundle/x.js \
  y.js -o bundle/y.js \
  > bundle/common.js

Whichever one of these 3 options, you take, you can now have 2 pages, each with a different combination of script tags but with all the common modules factored out into a common.js to avoid transferring the same code multiple times:

<script src="/bundle/common.js"></script>
<script src="/bundle/x.js"></script>
<script src="/bundle/common.js"></script>
<script src="/bundle/y.js"></script>

to verify this works from node you can do:

$ cat bundle/common.js bundle/x.js | node
$ cat bundle/common.js bundle/y.js | node

command-line outpipe example

We can pipe each output file through some other processes. Here we'll do minification with uglify compression with gzip:

browserify files/*.js \
    -p [ factor-bundle -o 'uglifyjs -cm | gzip > bundle/`basename $FILE`.gz' ] \
    | uglifyjs -cm | gzip > bundle/common.js.gz

api plugin example

If you prefer you can use the factor-bundle plugin api directly in code:

var browserify = require('browserify');
var fs = require('fs');

var files = [ './files/x.js', './files/y.js' ];
var b = browserify(files);
b.plugin('factor-bundle', { outputs: [ 'bundle/x.js', 'bundle/y.js' ] });

or instead of writing to files you can output to writable streams:

var browserify = require('browserify');
var concat = require('concat-stream');

var files = [ './files/x.js', './files/y.js' ];
var b = browserify(files);

b.plugin('factor-bundle', { outputs: [ write('x'), write('y') ] });

function write (name) {
    return concat(function (body) {
        console.log('// ----- ' + name + ' -----');


You can use factor-bundle as a browserify plugin:

browserify -p [ factor-bundle OPTIONS ]

where OPTIONS are:

  -o  Output FILE or CMD that maps to a corresponding entry file at the same
      index. CMDs are executed with $FILE set to the corresponding input file.
      Optionally specify a function that returns a valid value for this argument.

  -e  Entry file to use, overriding the entry files listed in the original

or you can use the command:

usage: factor-bundle [ x.js -o bundle/x.js ... ] > bundle/common.js

Read `module-deps` json output from stdin, factoring each entry file out into
the corresponding output file (-o).

  -o FILE, -o CMD

    Write output to FILE or CMD. CMD is distinguished from FILE by the presence
    of one or more `>` or `|` characters. For example, use:

      factor-bundle browser/a.js browser/b.js \
        -o bundle/a.js -o bundle/b.js

    to write to a FILE. And do something like:

      factor-bundle browser/*.js \
        -o 'uglifyjs -cm | gzip > bundle/`basename $FILE`.gz'

    to use a CMD. In the CMD, $FILE is set to the corresponding input file path.

    If there is a trailing unpaired `-o`, that file will be used for the common
    bundle output. Otherwise, the final bundle is written to stdout.


var factor = require('factor-bundle')

var fr = factor(files, opts={})

Return a transform stream tr that factors the array of entry path strings files out into bundle files. The input format that fr expects is described in the module-deps package.

The output format for fr and each of the fr sub-streams given by each 'stream' event is also in the module-deps format.

opts.o or opts.outputs should be an array that pairs up with the files array to specify where each bundle output for each entry file should be written. The elements in opts.o can be string filenames, writable streams, or functions that return a string filename or writable stream.

opts.entries or opts.e should be the array of entry files to create a page-specific bundle for each file. If you don't pass in an opts.entries, this information is gathered from browserify itself.

The files held in common among > opts.threshold (default: 1) bundles will be output on the fr stream itself. The entry-specific bundles are diverted into each 'stream' event's output. opts.threshold can be a number or a function opts.threshold(row, groups) where row is a module-deps object and groups is an array of bundles which depend on the row. If the threshold function returns true, that row and all its dependencies will go to the common bundle. If false, the row (but not its dependencies) will go to each bundle in groups. For example:

factor(files, {threshold: function(row, groups) {
    if (/.*a\.js$/.test(row.id)) return false;
    if (/.*[z]\.js$/.test(row.id)) return true;
    return this._defaultThreshold(row, groups);


fr.on('stream', function (stream) {})

Each entry file emits a 'stream' event containing all of the entry-specific rows that are only used by that entry file (when opts.threshold === 1, the default).

The entry file name is available as stream.file.

b.on('factor.pipeline', function (file, pipeline) {})

Emits the full path to the entry file (file) and a labeled-stream-splicer (pipeline) for each entry file with these labels:

You can call pipeline.get with a label name to get a handle on a stream pipeline that you can push(), unshift(), or splice() to insert your own transform streams.

Event handlers must be attached before calling b.plugin.


With npm do:

npm install factor-bundle