on-demand course

Mastering JavaScript Variable Declarations - Insights into VAR, LET, and CONST in 2025

with SkillZone

December 2024

Intermediate

5h 19m

English

Packt Publishing

Closed Captioning available in English

Watch now

Unlock full access

Includes

Earns Badge

Course outline

Course Introduction
3m 51s
Intro to Variables, Execution Context, Temporal Dead Zones, Scope, and More
5m 8s
Temporal Dead Zone
7m 41s
History of VAR, LET, and CONST
1m 59s
The 3 Stages of a Variable's Life, and the Million Dollar Question
3m 1s
Reasons Why JS Distinguishes Between Variable Declarations vs Initializations
11m 10s
Variable Hoisting
5m 8s
Using "Debugger" to Examine Scope of Functions and Variables
7m 24s
Why is VAR Initialized with the Value of "Undefined"?
2m 40s
VAR Allows Reassignment and Redeclaration, and Some Problems with VAR
7m 50s
LET Allows Reassignment but Not Redeclaration
3m 2s
CONST Prohibits Reassignment but Does Not Enforce Immutability
7m 57s
Scope Intro
1m 23s
Global Scope - VAR, LET, and CONST Are All Global Scoped. VAR Goes Further.
3m 40s
Why Adding Properties to the Global Object Is Generally Not a Good Idea
3m 19s
Function Scope - VAR, LET, and CONST
1m 59s
Comparing C and JavaScript Function Scope with VAR
9m 30s
Module Scope - VAR, LET, and CONST Are All Confined to Modules
6m 9s
Block Scope - LET and CONST Are Block Scoped
5m 31s
VAR Hacks, IIFEs, and "Use Strict"
7m 42s
VAR Is Not Block Scoped
2m 2s
Nested Scopes and Shadowing
3m 58s
Temporal Dead Zone - Why Was It Created?
6m 11s
What Does "Temporal" Mean in "Temporal Dead Zone"?
2m 34s
Example - Identifying Overall Scope
3m 13s
Example - Identifying Variable Scope
2m 19s
Example - Global Execution Context and the Call Stack
5m 17s
Example - Function Execution Context and the Call Stack
5m 41s
Example - Block Scope and Final Words
8m 6s
Does the JavaScript Engine Move Your Code Around?
2m 27s
Intro to VAR, and Execution Contexts
3m 11s
What You Are About to Learn Is Very Practical (and Advanced)
1m 58s
What Is an Execution Context (Phases and Types)?
9m 2s
Intro to the Realm Record
1m 39s
The 3 Most Important Fields That the Realm Record Creates
3m 1s
The [[Intrinsics]] Field
2m 58s
The [[GlobalObject]] Field
1m 57s
What Are Environment Records?
4m 27s
The [[GlobalEnv]] Field
7m 56s
Global Variable Recap
2m 31s
The [[VarNames]] Field, and Recap
9m 53s
Lexical and Variable Environment
1m 33s
Basic Example with a Blank app.js File
4m 50s
Example - Setting Up the Global Execution Context
4m 54s
Example - Assigning the Global Variables and Function to the Correct Fields
8m 50s
Function Object Intro
3m 45s
Execution Phase and the Call Stack
7m 58s
Example Execution - Part 1
6m 34s
Function Execution Context - How It Works Under the Hood
6m 14s
Example Execution - Part 2
4m 20s
Quasi Code Walkthrough from a Developer's Perspective
14m 59s
VAR Definition as per ECMAScript
5m 4s
LET Definition as per ECMAScript
6m 42s
What Happens If You Try and Redeclare a LET Variable
3m 53s
BLOCK Definition as per ECMAScript
4m 6s
BLOCK Example
5m 11s
Final Example to Drive the Point Home
2m 33s
Introduction to Scoping in JavaScript (with an Example)
4m 10s
Lexical Scoping vs Dynamic Scoping with Bash Example
9m 4s
CONST Variables and Immutability
5m 7s
Using CONST with Object.freeze() to Ensure True Immutability
4m 56s
Use Cases for VAR
6m 34s
Outro
1m 30s

Overview

In this 5-hour course, you'll learn to master JavaScript variable declarations: VAR, LET, and CONST. We'll dive into their behavior, scope, and usage through practical examples and debugging techniques, ensuring you gain a comprehensive understanding.

What I will be able to do after this course

Understand the scope, lifecycle, and behavior of JavaScript variables.
Differentiate the practical applications of VAR, LET, and CONST.
Utilize debugging tools to resolve JavaScript variable scope issues.
Write safer JavaScript code with modern declaration techniques.
Apply advanced concepts like immutability and scoping nuances.

Course Instructor(s)

Your instructor brings seasoned experience in JavaScript development and technical training. Having worked on numerous web application projects, they understand real-world challenges developers face. Their passion for teaching ensures a hands-on, practical learning experience.

Who is it for?

This course is tailored for developers with foundational JavaScript knowledge looking to deepen their understanding of variable declarations and scoping. Front-end and back-end developers aiming to improve code robustness and grasp modern features like LET and CONST will find this valuable.