c3/docs/js/samples/chart_step.js

var chart = c3.generate({
    data: {
        columns: [
            ['data1', 300, 350, 300, 0, 0, 100],
            ['data2', 130, 100, 140, 200, 150, 50]
        ],
        types: {
            data1: 'step',
            data2: 'area-step'
        }
    }
});