README.md

React Shallow Context

Pure shallow equal for update propagation in 300b.

Goal

This package optimizes React.Context API by implementing calculateChangedBits, which works the same way as shouldComponentUpdate or PureComponent - it optimizes the way React reacts to context updates.

The problem

It is common to store an object inside of the context Provider:

<Provider value={{key1: 1, key2: 2}} />

However, that produces a new value every time, causing all Consumers to update. React then needs to traverse the entire tree to find those Consumer components. This package provides a way to handle when the value changes, and suppress unnecessary updates.

API

createPureContext(defaultValue)

Creates "pure" context, the same way that "PureComponent" is "pure." This is equivalent to React.createContext(xx, pureContextCompare)

👎 import {createContext} from 'react';
const context = createContext();

👍 import {createPureContext} from 'react-shallow-context';
const context = createPureContext();

pureContextCompare

Shallow compares the old and next context value. It supresses the update if they are the same.

import {pureContextCompare} from 'react-shallow-context';
const context = React.createContext({}, pureContextCompare);

// equal to
const context = createPureContext({});

updateIgnoring(keys)

The same as pureContextCompare, but it ignores selected keys. This is useful when the context contains some callback function that could always be different, but only plays a role when another value is changed.

import {updateIgnoring} from 'react-shallow-context';
const context = React.createContext({importantValue, notImportantValue}, updateIgnoring(['notImportantValue']));

updateOnlyFor(keys)

The inverse of updateIgnoring. Will only trigger an update when the given keys change.

import {updateOnlyFor} from 'react-shallow-context';
const context = React.createContext({importantValue, notImportantValue}, updateOnlyFor(['importantValue']));

Licence

MIT