bulk-properties/demos/incrementDecrement.html at master · ComponentKitchen/bulk-properties · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>

  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width,initial-scale=1">
  <title>Increment/Decrement web component</title>
  <script type="module" src="../src/polyfill.js"></script>

  <template id="template">
    <button id="decrement">-</button>
    <span id="value"></span>
    <button id="increment">+</button>
  </template>

  <script type="module">

    class IncrementDecrement extends HTMLElement {

      constructor() {
        super();
        this.state = {
          max: 5,
          min: -5,
          value: 0
        };
      }

      connectedCallback() {
        this.attachShadow({ mode: 'open' });
        const instance = document.importNode(template.content, true);
        instance.querySelector('#decrement').addEventListener('click', () => {
          this.value--;
        });
        instance.querySelector('#increment').addEventListener('click', () => {
          this.value++;
        });
        this.shadowRoot.appendChild(instance);
        this.render();
      }

      render() {
        const value = this.state.value;
        this.shadowRoot.applyPropertiesById({
          decrement: {
            attributes: {
              disabled: value <= this.state.min
            }
          },
          increment: {
            attributes: {
              disabled: value >= this.state.max
            }
          },
          value: {
            style: {
              color: value < 0 ? 'red' : null
            },
            textContent: value
          }
        });
      }

      setState(changes) {
        Object.assign(this.state, changes);
        this.render();
      }

      get value() {
        return this.state.value;
      }
      set value(value) {
        this.setState({ value });
      }

    }

    customElements.define('increment-decrement', IncrementDecrement);
  </script>

</head>

<body>
  <increment-decrement></increment-decrement>
</body>

</html>