Lesson: Introduction to JavaScript – Create a Variable: let

Learning Objectives

1. Understand the difference between const and let in JavaScript.
2. Learn how to declare a variable using let.
3. Understand when to use let versus const.

Lesson Content – Introduction to JavaScript – Create a Variable let

1. Constants (const)

The const keyword is used to declare variables whose values cannot be reassigned after their initial assignment.

Example:

Error: Introduction to JavaScript – Create a Variable let

const ensures that the value remains constant throughout the program. It is generally used for values that should not change, such as configuration constants or fixed references.

2. Mutable Variables (let)

The let keyword is used to declare variables whose values can be reassigned.

Example:

Here, the variable meal is declared using let and can be updated with a new value later in the program.

3. When to Use const vs let

• Use const when the value of a variable should not change.
  • Example: Fixed settings like const PI = 3.14;
• Use let when the value of a variable is expected to change.
  • Example: Temporary or changing states like let score = 0;

Code Examples – Introduction to JavaScript – Create a Variable let

Here are additional examples to reinforce the concepts:

Example 1: Using const

Example 2: Using let

Example 3: When to Use const and let

Assignment

Write a program that does the following:

1. Declare a variable using const to store your favorite fruit.
2. Attempt to reassign the const variable to a new fruit and observe the error in the console.
3. Declare a variable using let to store your favorite drink.
4. Reassign the let variable to a new drink and log both the old and new values to the console.

Answer Key

Here’s a possible solution for the assignment:

Key Takeaways – Introduction to JavaScript – Create a Variable let

• Use const when the value should remain constant.
• Use let when the value needs to be reassigned.

Assignment Ideas: a. Modify the assignment to include examples of var and explain why it’s less commonly used in modern JavaScript.
b. Create a quiz on const and let to test comprehension.

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