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    Deep Learning in Javascript. Train Convolutional Neural Networks (or ordinary ones) in your browser.
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    • 🕩2026
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    ConvNetJS is a Javascript implementation of Neural networks, together with nice browser-based demos. It currently supports:

    • Common Neural Network modules (fully connected layers, non-linearities)
    • Classification (SVM/Softmax) and Regression (L2) cost functions
    • Ability to specify and train Convolutional Networks that process images
    • An experimental Reinforcement Learning module, based on Deep Q Learning

    For much more information, see the main page at

    Note: I am not actively maintaining ConvNetJS anymore because I simply don't have time. I think the npm repo might not work at this point.

    Online Demos

    Example Code

    Here's a minimum example of defining a 2-layer neural network and training it on a single data point:

    // species a 2-layer neural network with one hidden layer of 20 neurons
    var layer_defs = [];
    // input layer declares size of input. here: 2-D data
    // ConvNetJS works on 3-Dimensional volumes (sx, sy, depth), but if you're not dealing with images
    // then the first two dimensions (sx, sy) will always be kept at size 1
    layer_defs.push({type:'input', out_sx:1, out_sy:1, out_depth:2});
    // declare 20 neurons, followed by ReLU (rectified linear unit non-linearity)
    layer_defs.push({type:'fc', num_neurons:20, activation:'relu'}); 
    // declare the linear classifier on top of the previous hidden layer
    layer_defs.push({type:'softmax', num_classes:10});
    var net = new convnetjs.Net();
    // forward a random data point through the network
    var x = new convnetjs.Vol([0.3, -0.5]);
    var prob = net.forward(x); 
    // prob is a Vol. Vols have a field .w that stores the raw data, and .dw that stores gradients
    console.log('probability that x is class 0: ' + prob.w[0]); // prints 0.50101
    var trainer = new convnetjs.SGDTrainer(net, {learning_rate:0.01, l2_decay:0.001});
    trainer.train(x, 0); // train the network, specifying that x is class zero
    var prob2 = net.forward(x);
    console.log('probability that x is class 0: ' + prob2.w[0]);
    // now prints 0.50374, slightly higher than previous 0.50101: the networks
    // weights have been adjusted by the Trainer to give a higher probability to
    // the class we trained the network with (zero)

    and here is a small Convolutional Neural Network if you wish to predict on images:

    var layer_defs = [];
    layer_defs.push({type:'input', out_sx:32, out_sy:32, out_depth:3}); // declare size of input
    // output Vol is of size 32x32x3 here
    layer_defs.push({type:'conv', sx:5, filters:16, stride:1, pad:2, activation:'relu'});
    // the layer will perform convolution with 16 kernels, each of size 5x5.
    // the input will be padded with 2 pixels on all sides to make the output Vol of the same size
    // output Vol will thus be 32x32x16 at this point
    layer_defs.push({type:'pool', sx:2, stride:2});
    // output Vol is of size 16x16x16 here
    layer_defs.push({type:'conv', sx:5, filters:20, stride:1, pad:2, activation:'relu'});
    // output Vol is of size 16x16x20 here
    layer_defs.push({type:'pool', sx:2, stride:2});
    // output Vol is of size 8x8x20 here
    layer_defs.push({type:'conv', sx:5, filters:20, stride:1, pad:2, activation:'relu'});
    // output Vol is of size 8x8x20 here
    layer_defs.push({type:'pool', sx:2, stride:2});
    // output Vol is of size 4x4x20 here
    layer_defs.push({type:'softmax', num_classes:10});
    // output Vol is of size 1x1x10 here
    net = new convnetjs.Net();
    // helpful utility for converting images into Vols is included
    var x = convnetjs.img_to_vol(document.getElementById('some_image'))
    var output_probabilities_vol = net.forward(x)

    Getting Started

    A Getting Started tutorial is available on main page.

    The full Documentation can also be found there.

    See the releases page for this project to get the minified, compiled library, and a direct link to is also available below for convenience (but please host your own copy)

    Compiling the library from src/ to build/

    If you would like to add features to the library, you will have to change the code in src/ and then compile the library into the build/ directory. The compilation script simply concatenates files in src/ and then minifies the result.

    The compilation is done using an ant task: it compiles build/convnet.js by concatenating the source files in src/ and then minifies the result into build/convnet-min.js. Make sure you have ant installed (on Ubuntu you can simply sudo apt-get install it), then cd into compile/ directory and run:

    $ ant -lib yuicompressor-2.4.8.jar -f build.xml

    The output files will be in build/

    Use in Node

    The library is also available on node.js:

    1. Install it: $ npm install convnetjs
    2. Use it: var convnetjs = require("convnetjs");



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