See the WEKA wiki for details on the file format.
First, install node.js and get the node-arff NPM module using npm:
$ npm install node-arff
Then, get yourself an ARFF file (http:https://axon.cs.byu.edu/data/ has a few) to read.
var arff = require('node-arff');
arff.load('data/some-file.arff', function(err, data) {
if (err) {
return console.error(err);
}
// find out some info about the field "age"
var oldest = data.max('age');
var youngest = data.min('age');
var mostcommon = data.mode('age');
var average = data.mean('age');
// normalize the data (scale all numeric values so that they are between 0 and 1)
data.normalize();
// randomly sort the data
data.randomize();
})