使用defineproperty來定義setter、getter來進行攔截與更新Dom
Html:

<input id = 'input1' />
<input id = 'input2' />

JavaScrpt:

let model = { value: '' };
let vm = {};
Reflect.defineProperty(vm, 'value', {
  set(newValue) {
    Reflect.set(model, 'value', newValue);
    document.getElementById('input2').value = newValue;
    document.getElementById('input1').value = newValue;
  },
  get() {
    return Reflect.get(model, value);
  }
})
document.getElementById('input1').addEventListener('input', (e) => {
  vm.value = e.target.value;
})
document.getElementById('input2').addEventListener('input', (e) => {
  vm.value = e.target.value;
})