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Friday, March 10, 2017

React, Redux and Immutable.js

React, Redux and Immutable.js are currently among the most popular JavaScript libraries and are rapidly becoming developers’ first choice when it comes to front-end development. In the few React/Redux projects that I have worked on, I realised that a lot of developers getting started with React do not fully understand React and how to write efficient code to utilise its full potential.
Some of the most common misuses of React and ways to avoid them.

Data Reference Problem
Any React app should mostly consist of small simple (or stateless function) components. They are simple to reason about and most of them can have shouldComponentUpdate function returning false.

shouldComponentUpdate(nextProps, nextState) { return false; }

Performance wise, the most important component lifecycle function is shouldComponentUpdate and if possible it should always return false. This ensures that this component will never re-render (except the initial render) effectively making the React app feel extremely fast.

Equality check for primitive data types like boolean, string and integer is very simple since they are always compared by their actual value:

1 === 1
’string’ === ’string’
true === true

On the other hand, equality check for complex types like objects, arrays and_functions_ is completely different. Two objects are the same if they have the same reference (pointing to the same object in memory).

const obj1 = { prop: ’someValue’ };
const obj2 = { prop: ’someValue’ };
console.log(obj1 === obj2);   // false

Even though obj1 and obj2 appear to be the same, their reference is different. Since they are different, comparing them naively within the shouldComponentUpdate function will cause our component re-render needlessly.

Handling References
This is not an easy task if we want to do it in a nice, clean, and performance optimised way. Facebook realised this problem a long time ago and called Immutable.js to the rescue.

import { Map } from ‘immutable’;

//  transform object into immutable map
let obj1 = Map({ prop: ’someValue’ });  
const obj2 = obj1;
console.log(obj1 === obj2);  // true

obj1 = obj1.set(‘prop’, ’someValue’);  // set same old value
console.log(obj1 === obj2);  // true | does not break reference because nothing has changed 

obj1 = obj1.set(‘prop’, ’someNewValue’);   // set new value
console.log(obj1 === obj2);  // false | breaks reference 
obj1 = obj1.set(...);.
See the full article here

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