react/docs/tips/08-controlled-input-null-value.md

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controlled-input-null-value	Value of null for Controlled Input	tips	tips/controlled-input-null-value.html	children-props-type.html	componentWillReceiveProps-not-triggered-after-mounting.html

Specifying the value prop on a controlled component prevents the user from changing the input unless you desire so.

You might have run into a problem where value is specified, but the input can still be changed without consent. In this case, you might have accidentally set value to undefined or null.

The snippet below shows this phenomenon; after a second, the text becomes editable.

ReactDOM.render(<input value="hi" />, mountNode);

setTimeout(function() {
  ReactDOM.render(<input value={null} />, mountNode);
}, 1000);