This course is designed to provide in-depth knowledge of JavaScript variable declarations, focusing on the differences between VAR, LET, and CONST. By the end of this course, learners will have a clear understanding of how these declarations affect variable scope, execution contexts, and best practices in modern JavaScript development. This knowledge is crucial for writing cleaner, more efficient code and avoiding common pitfalls that developers face when handling variables.



Mastering JavaScript Variables – VAR, LET & CONST in 2025

Instructor: Packt - Course Instructors
Included with
Recommended experience
What you'll learn
Understand the three stages in a variable's lifecycle and how they affect variable behavior.
Explore the differences between VAR, LET, and CONST, and how each handles scoping and hoisting.
Learn how to use JavaScript's execution contexts and apply debugging techniques effectively.
Gain a solid understanding of block, function, and global scope in JavaScript with practical examples.
Skills you'll gain
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May 2025
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There are 6 modules in this course
In this module, we will introduce you to the fundamental concepts of JavaScript variables, including execution context, scope, and temporal dead zones. You'll explore how different variable declarations, such as VAR, LET, and CONST, interact within various scopes, and how hoisting affects their behavior. By the end, you'll be equipped to understand and manage JavaScript's variable lifecycle and scope in your applications.
What's included
29 videos1 reading1 assignment
In this module, we will dive into the creation phase of JavaScript's execution context, breaking down the internal processes of how the engine sets up variables and functions. You'll explore the critical role of the Realm Record, Environment Records, and other key fields in this phase. Through practical examples, you'll gain a deep understanding of how JavaScript organizes and manages execution contexts to handle your code effectively.
What's included
17 videos1 assignment
In this module, we will explore the execution phase of JavaScript’s execution context, focusing on the call stack and how it manages the execution of code. Through detailed examples, you'll gain insights into how function execution contexts are formed and executed. By the end, you'll be able to follow code execution step-by-step, understanding the inner workings of JavaScript at runtime.
What's included
5 videos1 assignment
In this module, we will focus on the differences between VAR, LET, and CONST, as defined by ECMAScript, and explore how they function in relation to block scope. You'll learn the specific rules around redeclaration, especially for LET, and understand how block-level scope works with practical examples. By the end of this section, you'll have a solid grasp of how these variable types interact with blocks in JavaScript.
What's included
6 videos1 assignment
In this module, we will introduce the concepts of lexical and dynamic scoping, explaining their key differences. Through examples, you'll see how JavaScript uses lexical scoping to determine variable resolution and how this contrasts with dynamic scoping, particularly in the context of Bash. By the end, you'll be able to understand and navigate scoping rules in both languages.
What's included
2 videos1 assignment
In this final module, we will wrap up by discussing immutability with CONST, exploring how Object.freeze() can help achieve true immutability in objects. You'll also review the use cases for VAR in today's JavaScript environment, ensuring you understand when and why to use it. The module concludes with a summary of key concepts covered throughout the course.
What's included
4 videos2 assignments
Instructor

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Frequently asked questions
Yes, you can preview the first video and view the syllabus before you enroll. You must purchase the course to access content not included in the preview.
If you decide to enroll in the course before the session start date, you will have access to all of the lecture videos and readings for the course. You’ll be able to submit assignments once the session starts.
Once you enroll and your session begins, you will have access to all videos and other resources, including reading items and the course discussion forum. You’ll be able to view and submit practice assessments, and complete required graded assignments to earn a grade and a Course Certificate.
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