const {div, label, input, h2, makeDOMDriver } = CycleDOM;

​

function main(sources) {

  const weightChange$ = sources.DOM.select('.weight').events('input').map(evt => evt.target.value);

  const heightChange$ = sources.DOM.select('.height').events('input').map(evt => evt.target.value);

  const bmi$ = Rx.Observable.combineLatest(

                  weightChange$.startWith(70), 

                  heightChange$.startWith(170), 

                  (weight, height) => {

                    const heightMeters = height * 0.01;

                    const bmi = Math.round(weight / (heightMeters * heightMeters));

                    return {bmi, weight, height};

                  });

  return {

    DOM: bmi$.map(({bmi, weight, height}) => 

           div([

             div([

               label(`Weight: ${weight} kg`),

               input('.weight', {type: 'range', min: 40, max: 150, value: weight})

             ]),

             div([

               label(`Height: ${height} cm`),

               input('.height', {type: 'range', min: 140, max: 220, value: height})

             ]),

             h2(`BMI is ${bmi}`)

           ]))

  };

}

​

const drivers = {

  DOM: makeDOMDriver('#app')

};

​

Cycle.run(main, drivers);