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UnuglifyJS is a JavaScript tool that renames variables and parameters to names based on statistical model learnt from thousands of open source projects. This is on open-source reimplementation of the JS Nice tool which provides similar functionality.

The implementation of UnuglifyJS is based on UglifyJS 2 -- parser, minifier, compressor or beautifier toolkit for JavaScript.

This page documents how to use the UnuglifyJS as a client of the Nice 2 Predict framework to build statistical model learnt from thousands of open source projects, which is subsequently used to rename variables and parameters names of minified JavaScript files. A live demo of the Unuglify client is available at

NPM Module

The npm module is available at To install run:

sudo npm install unuglify-js --global

To use the UnuglifyJS simply supply the JavaScript file to be analyzed. For example:

//demo.js - minified file
function f(a,b,c) {'GET', a, false);

unuglifyjs demo.js > demo_renamed.js

function f(fileUrl, req, message) {'GET', fileUrl, false);

Install from Source


First make sure you have installed the latest version of node.js and NPM. (You may need to restart your computer after this step).

sudo apt-get install nodejs npm

Download UnuglifyJS git repository:

git clone

Once the sources are downloaded, install all the dependencies using NPM:

sudo npm install

(Optional) Check that everything is installed correctly by running the tests:


(Optional) Package for the browser. The UglifyJS2 provides a quick way to build itself for the browser using followig command:

bin/unuglifyjs --package > /tmp/uglify.js

Nice 2 Predict

To install Nice 2 Predict framework please follow the instructions on the page.

Obtaining Training Dataset (UnuglifyJS)

As a first step we need to obtain a large number of JavaScript files that can be used to train the statistical model. This can be easily achieved by downloading large amount of projects from GitHub or other repositories.

To produce the training dataset, from the UnuglifyJS directory run the following script:

./ --dir . > training_data

Here, the --dir . is used to specify which directory is searched for JavaScript files. In this demo we simply use the source files of the UnuglifyJS itself. While the script is runnig, you might notice output such as Skipping minified file: './test/compress/issue-611.js'. This is because our goal is to predict good variable names, therefore we do not want to train on already minified files.

Before we discuss how to train the statistical model, we briefly describe how the programs are represented and the format of the training dataset.

Program Representation

The role of the Unuglify client to perform a program analysis which transforms the input program into a representation that allows usage of machine learning algorithms provided by Nice 2 Predict. Here, the program is represented as a set of features that relate known and unknown properties of the program. We illustrate the program representation using the following code snippet var a = s in _MAP; where _MAP is a global variable.

  • Known properties are program constants, objects properties, methods and global variables – that is, program parts which cannot be (soundly) renamed (e.g. the DOM APIs). The known properties of the code snippet are:


  • Unknown properties are all local variables. The unknown properties of the code snippet are:

    a, s

  • Features relate properties. An example of feature function is (s, _MAP) -> :Binaryin: between properties s and _MAP, which captures the fact that they are used together as a left-hand and right-hand side of binary operator in. The features of the code snippet are:

	(a, s) -> :VarDef:Binaryin[0]
	(a, _MAP) -> :VarDef:Binaryin[1]
	(s, _MAP) -> :Binaryin:
Program Format

The program representation as described above is translated into a JSON format which the Nice2Predict server can process. The JSON consists of two parts query describing the features and assign describing the properties and their initial assignments with the attribute giv or inf for known and unknown properties respectively. That is, the JSON representation of the code snippet var a = s in _MAP; is:

  {"a": 0,	"b": 1,	"f2": ":VarDef:Binaryin[0]"},
  {"a": 0,	"b": 2,	"f2": ":VarDef:Binaryin[1]"},
  {"a": 1,	"b": 2,	"f2": ":Binaryin:"}
  {"v": 0,	"inf": "a"},
  {"v": 1,	"inf": "s"},
  {"v": 2,	"giv": "_MAP"}
Training Dataset Format

The training dataset produced by running UnuglifyJS simply consists of JSON program representations as shown above, one per line.

Training (Nice2Predict)

Succesfull compilation of Nice2Predict creates a training binary in Nice2Predict installation directory. To train to model we simply run:

bazel run n2p/training/train_json -- --logtostderr -num_threads 16 --input path/to/training_data

where training_data is the file produced in previous step and num_threads specifies how many threads should the training algorithm use. To get full options available for training (such as learning rate, regularization and margin), use:

bazel run n2p/training/train_json -- --help

After the training finishes, two files are created which contains the trained model: model_strings and model_features.

Predicting Properties (Nice2Predict)

To predict properties for new programs, start a server after a model was trained:

bazel run n2p/json_server/json_server -- --logtostderr --model=$PWD/model

Then, the server will predict properties for programs given in JsonRPC format. One can debug and observe deobfuscation from the viewer available in the viewer/viewer.html (online demo available at The server takes as an input same JSON format as described above and returns best assigment to the unknown properties (labelled as inf).

Changing UnuglifyJS

When changing the features of Unuglify js, you may want to use the Nice2Predict viewer to see the updates. The Nice2Predict viewer calls UnuglifyJS from the browser, not from nodeJS. To update its viewer run:

bin/unuglifyjs --package > /tmp/uglify.js cp /tmp/uglify.js <path_to_nice2predict>/viewer/uglifyjs/uglify.js


A simpler open-source version of JavaScript deobfuscator JSNice









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