Shallow Compare

Note:

shallowCompare is a legacy add-on. Use React.memo or React.PureComponent instead.

Importing

import shallowCompare from 'react-addons-shallow-compare'; // ES6
var shallowCompare = require('react-addons-shallow-compare'); // ES5 with npm

Overview

Before React.PureComponent was introduced, shallowCompare was commonly used to achieve the same functionality as PureRenderMixin while using ES6 classes with React.

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 helper function for a performance boost in some cases.

Example:

export class SampleComponent extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    return shallowCompare(this, nextProps, nextState);
  }

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

shallowCompare performs a shallow equality check on the current props and nextProps objects as well as the current state and nextState objects. It does this by iterating on the keys of the objects being compared and returning true when the values of a key in each object are not strictly equal.

shallowCompare returns true if the shallow comparison for props or state fails and therefore the component should update. shallowCompare returns false if the shallow comparison for props and state both pass and therefore the component does not need to update.