Life Coding - JavaScript Immutability

1. Lecture Introduction

The JavaScript Immutability class of Life Coding is a lecture on how to handle data immutably in JavaScript. It is aimed at learners who know the basic grammar of JavaScript and looks at how to prevent the original from being damaged by making data immutable.

This course covers the following topics:

• Differences between how primitive data types and objects behave
• How to clone an object
• How to modify a clone without modifying the original object

The following is not covered:

• Immutable library

2. Lecture Target

Treating data as immutable can drastically reduce the possibility of bugs caused by interference between data. It also makes it very easy to check whether data has changed. It also serves as a basis for implementing advanced techniques such as hot module reloading and time travel.

If you can predict the results of all the code below, you don't need to take this class.

var n1 = 1;
var n2 = 1;
console.log(n1 === n2);
=> It is true. Of course.

var o1 = {name:'kim'}
var o2 = {name:'kim'}
console.log(o1 === o2);
=> false . It's a bit ambiguous. JavaScript treats primitive data types, whose values cannot change, differently from objects, whose values can change.

var o1 = {name:'kim'}
var o2 = o1;
o2.name = 'lee';
console.log(o1.name);
=> This is lee. o1 doesn't know English and the value of the name it is pointing to has changed.

var o1 = {name:'kim'}
var o2 = Object.assign({}, o1); // Copy o1 to an empty object.
o2.name = 'lee';
console.log(o1.name);
=> This is kim. Even if o2 is changed, o1 is not affected. o1 can remain in an invariant state with respect to o2.

var o1 = {score:[1,2]}
var o2 = Object.assign({}, o1);
o2.score.push(3);
console.log(o1.score)
=> It's [1,2,3]. I don't know English, and o1 changed again. This is because score is an array, which is a type of object.

var o1 = {score:[1,2]}
var o2 = Object.assign({}, o1);
o2.score = o2.score.concat(); // Copy the array.
o2.score.push(3);
console.log(o1.score)
=> It is [1,2].

There is another way, which is to copy everything.
var o1 = {score:[1,2]}
var o2 = JSON.parse(JSON.stringify(o1));
o2.score.push(3);
console.log(o1.score)
=> It is [1,2].

It's a good idea to be careful not to change the original, but it's also possible to prevent the original from changing at all.
var o1 = {name:'kim'}
Object.freeze(o1);
o1.name = 'lee';
console.log(o1.name);
=> It's 'kim'.

But objects can't do this.
var o1 = {score:[1,2]}
Object.freeze(o1);
o1.score.push(3);
console.log(o1.score);
// It is [1,2,3].

Defensive freezing is required.
var o1 = {score:[1,2]}
Object.freeze(o1);
Object.freeze(o1.score);
o1.score.push(3);
console.log(o1.score);
// It doesn't change anything. It even causes a protest error.

3. Conditions for participation in the lecture

To take this course, you need the following prerequisite knowledge:
(You can study either one.)

• JavaScript ( WEB2 JavaScript class )
• NodeJS ( WEB2 Nodejs class )

4. Total playback time

This is a one-hour class consisting of 12 videos.

5. Copyright of the class

This lecture is licensed under a Creative Commons license and can also be viewed at the link below.
https://opentutorials.org/module/4075 I would like to thank Life Coding for sharing good knowledge.