react.dev/docs/10.7-pure-render-mixin.md

id	title	permalink	prev	next
pure-render-mixin	PureRenderMixin	pure-render-mixin.html	update.html	perf.html

If your React component's render function is "pure" (in other words, it renders the same result given the same props and state), you can use this mixin for a performance boost in some cases.

Example:

var PureRenderMixin = require('react').addons.PureRenderMixin;
React.createClass({
  mixins: [PureRenderMixin],

  render: function() {
    return <div className={this.props.className}>foo</div>;
  }
});

Under the hood, the mixin implements shouldComponentUpdate, in which it compares the current props and state with the next ones and returns false if the equalities pass.

Note:

This only shallowly compares the objects. If these contain complex data structures, it may produce false-negatives for deeper differences. Only mix into components which have simple props and state, or use forceUpdate() when you know deep data structures have changed. Or, consider using immutable objects to facilitate fast comparisons of nested data.

Furthermore, shouldComponentUpdate skips updates for the whole component subtree. Make sure all the children components are also "pure".