[js] 버튼 클릭 시 숫자 증가 증감

<div id="counter">0</div>

  <button id="increase">+</button>

  <button id="decrease">-</button>

  <script>

    const $counter = document.getElementById('counter');

    const $increase = document.getElementById('increase');

    const $decrease = document.getElementById('decrease');

    let num = 0;

    const render = function() {$counter.innerHTML = num;};

    $increase.onclick = function(){

      num++;

      console.log('increase 버튼클릭', num);

      render();

    };

    $decrease.onclick = function(){

      num--;

      console.log('decrease 버튼 클릭', num);

      render();

    };

  </script>