Packt
Mastering JavaScript Variables – VAR, LET & CONST in 2025
Packt

Mastering JavaScript Variables – VAR, LET & CONST in 2025

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Gain insight into a topic and learn the fundamentals.
Intermediate level

Recommended experience

7 hours to complete
3 weeks at 2 hours a week
Flexible schedule
Learn at your own pace
Gain insight into a topic and learn the fundamentals.
Intermediate level

Recommended experience

7 hours to complete
3 weeks at 2 hours a week
Flexible schedule
Learn at your own pace

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.

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Recently updated!

May 2025

Assessments

7 assignments

Taught in English

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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

Packt - Course Instructors
Packt
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