const doc = {
    baseInput: document.querySelector('#base'),
    heightInput: document.querySelector('#height'),
    areaInput: document.querySelector('#area'),
    calcButton: document.querySelector('#calcButton')
}

const state = {
    base: 0,
    height: 0,
    area: 0
}

doc.calcButton.addEventListener('click', () => {
    startCalc()
})

function startCalc() {
    state.base = doc.baseInput.value
    state.height = doc.heightInput.value
    state.area = calcArea(state.base, state.height)
    renderResult()
}

function calcArea(base, height) {
    return base * height / 2
}

function renderResult() {
    doc.baseInput.value = ''
    doc.heightInput.value = ''    
    doc.areaInput.value = state.area
    doc.baseInput.focus();
}