You need to have installed grunt-cli and npm, and have a stable Node.js version >= 0.8.0 on your system. (See gruntJS)
Ensure you have npm installed and up-to-date by running npm update -g npm, and install grunt-cli using npm install -g grunt-cli.
Then, while in the root simpleDOM directory, run the following commands:
npm install
grunt
This will minify src/simpledom.js and run the appropriate tests on it.