Binding Inputs to an Object in React

Let the state store an object:

jsxconst initObj = {
  prop1: 'value1',
  prop2: 'value2',
  prop3: 'value3',
}

function App() {
  const [obj, setObj] = useState(initObj);
  
  return <div>
    {obj.prop1}-{obj.prop2}-{obj.prop3}
  </div>;
}

Let's output each property of our object in a separate input:

jsxfunction App() {
  const [obj, setObj] = useState(initObj);
  
  return <div>
    <input value={obj.prop1} />
    <input value={obj.prop2} />
    <input value={obj.prop3} />
    
    <br />
    {obj.prop1}-{obj.prop2}-{obj.prop3}
  </div>;
}

Let's now bind the onChange event to each input. As a handler, we'll assign one common function:

jsxfunction App() {
  const [obj, setObj] = useState(initObj);
  
  return <div>
    <input value={obj.prop1} onChange={event => handleChange('prop1', event)} />
    <input value={obj.prop2} onChange={event => handleChange('prop2', event)} />
    <input value={obj.prop3} onChange={event => handleChange('prop3', event)} />
    
    <br />
    {obj.prop1}-{obj.prop2}-{obj.prop3}
  </div>;
}

As you can see, the handleChange function takes the name of the corresponding property of the object as its first parameter.

Let's write the implementation of our function:

jsxfunction handleChange(prop, event) {
  const copy = Object.assign({}, obj);
  copy[prop] = event.target.value;
  setObj(copy);
}

This implementation works, but it can be simplified by using computed names of object properties:

jsxfunction handleChange(prop, event) {
  setObj({...obj, ...{[prop]: event.target.value}});
}

Let's put all the code together:

jsxfunction App() {
  const [obj, setObj] = useState(initObj);
  
  function handleChange(prop, event) {
    setObj({...obj, ...{[prop]: event.target.value}});
  }
  
  return <div>
    <input value={obj.prop1} onChange={event => handleChange('prop1', event)} />
    <input value={obj.prop2} onChange={event => handleChange('prop2', event)} />
    <input value={obj.prop3} onChange={event => handleChange('prop3', event)} />
    
    <br />
    {obj.prop1}-{obj.prop2}-{obj.prop3}
  </div>;
}

jsxconst initDate = {
  year:  2025,
  month: 12,
  day:   31,
}