style-equal

An efficient equality algorithm for React Native inline styles

Why

shouldComponentUpdate is a powerful way to improve performance of react and react native applications, but often you will want to allow for a component to have a style prop to make the style of something be configurable.

Since style in react native can be of many forms (an object, a number, an array of both, or a nested array of both), it is not trivial or practical to implement an equality test for these props in the shouldComponentUpdate method.

Installation

npm i style-equal --save

Usage

import styleEqual from 'style-equal';

// ...

shouldComponentUpdate(nextProps) {
  return !styleEqual(this.props.style, nextProps.style);
}

Caveats

The styleEqual algorithm is implemented to be fast and efficient for usage with shouldComponentUpdate methods in react. The algorithm will never give a false-positive (ie, saying two things are equal when they are not), however, there are things that are semantically equivalent that the algorithm will return false for. One example of this is when comparing two styles such as:

styleEqual([1, false, 2], [1, 2]) // returns false

The above will always render the same styles, however the algorithm is built to assume that the position of a style will not change "slots" of the array.