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To get the value of an input field in React:

1. Declare a state variable that tracks the value of the input field.
2. Adds onChangea property to the input field.
3. Use event.target.valueto get the value of the input field and update the state variable.

import {useState} from 'react';

const App = () => {
  const [message, setMessage] = useState('');

  const handleChange = event => {
    setMessage(event.target.value);

    console.log('value is:', event.target.value);
  };

  return (
    <div>
      <input
        type="text"
        id="message"
        name="message"
        onChange={handleChange}
        value={message}
      />

      <h2>Message: {message}</h2>
    </div>
  );
};

export default App;

We use the useState hook to track the value of the input field.

We set onChangethe property on the field, so every time its value changes, handleChangethe function will be called.

We can access the value of the input element handleChangein the function as .event.target.value

eventThe object's targetproperties refer to the input elements.

handleChangeWe can access the value of the input field from anywhere outside the function using the message status variable .

Alternatively, we can use an uncontrolled input field.

To get the value of an uncontrolled input field in React:

1. Use useRefthe hook to initialize a ref.
2. Set the ref attribute on the input field.
3. ref.current.valueAccess the value of an input field as .

import {useRef} from 'react';

const App = () => {
  const inputRef = useRef(null);

  function handleClick() {
    console.log(inputRef.current.value);
  }

  return (
    <div>
      <input
        ref={inputRef}
        type="text"
        id="message"
        name="message"
      />

      <button onClick={handleClick}>Log message</button>
    </div>
  );
};

export default App;

This example uses an uncontrolled input. Note that the input field has no onChangeor valueattributes set.

We can use defaultValuethe attribute to pass an initial value to an uncontrolled input. However, this is not required and we can omit the attribute if we do not want to set an initial value.

When using uncontrolled input fields, we access the input using a ref.

useRef()The hook can be passed an initial value as an argument. The hook returns a mutable ref object whose .current property is initialized to the passed argument.

注意, we have to access the current property of the ref object to access the input element on which we set the ref attribute.

When we pass a ref prop to an element, for example <input ref={myRef} />, React .currentsets the property of the ref object to the corresponding DOM node.

useRefThe hook creates a normal JavaScript object, but gives us the same ref object on every render. In other words, it's a .currentmemoized object value with a ref property.

It is important to note that when we change the value of the ref's current attribute, it does not cause a re-render.

Each time the user clicks the button in the example, the uncontrolled input value is logged.

We should not set the value prop on uncontrolled inputs ( onChangeinput fields without a handler) because this will make the input field immutable and we won't be able to type in it.