Require is not defined in cordova project

In ubuntu 14.04 start installing all tools:

sudo apt-add-repository ppa:cordova-ubuntu/ppa
sudo apt-get update
sudo apt-get install cordova-cli ant ant-contrib ant-optional ant-gcj
sudo npm install -g cordova
sudo chown -R $USER /usr/local/lib/node_modules/cordova

Verify installation:

$ cordova --version ; node --version ; npm --version
3.5.0-0.2.7
v0.10.25
1.3.10

In ~/.bashrc add vars:

export ANDROID_HOME="/usr/share/android-studio/data/sdk/tools"
export ANDROID_PLATFORM_TOOLS="/usr/share/android-studio/data/sdk/platform-tools"
export PATH="$ANDROID_HOME:$ANDROID_PLATFORM_TOOLS:$PATH"

export ANT_HOME="/usr/share/ant"
export PATH="$PATH:$ANT_HOME/bin"

Now make the project:

cordova create demoApp com.demos.demoApp DEMOAPP
cd demoApp
cordova platform add android

In the index.js put the code:

try{
    var fs = require('fs');
}catch(e){
    alert(e.message);
}

But app says:

require is not defined

I did wrong?