react.dev/cookbook/cb-08-controlled-input-null-value tip.md

id	title	layout	permalink
controlled-input-null-value-tip	Value of null for controlled input	docs	controlled-input-null-value-tip.html

With a controlled input component, specifying a value prevents the user from changing the input unless you desire so (more info here).

You might have run into a problem where you specified a value but the input can still be changed. In this case, you might have accidentally set your value to undefined or null. The snippet below shows this phenomenon; after a second, the text can be edited.

/** @jsx React.DOM */

React.renderComponent(<input value="hi" />, mountNode);

setTimeout(function() {
  React.renderComponent(<input value={null} />, mountNode);
}, 2000);