In this section, we will explore the fundamental concepts of variables and data types in JavaScript. Understanding these concepts is crucial as they form the building blocks for writing any JavaScript program.

Variables are containers for storing data values. In JavaScript, you can declare a variable using the var, let, or const keywords.

1. Using var:

   var name = "John";
   console.log(name); // Output: John
   

2. Using let:

   let age = 25;
   console.log(age); // Output: 25
   

3. Using const:

   const pi = 3.14;
   console.log(pi); // Output: 3.14
   

• Scope: var is function-scoped, while let and const are block-scoped.
• Reassignment: const variables cannot be reassigned after their initial assignment.
• Hoisting: var declarations are hoisted to the top of their scope, while let and const are not.

JavaScript supports various data types, which can be categorized into two main types: Primitive and Reference.

1. String:

   let greeting = "Hello, World!";
   console.log(greeting); // Output: Hello, World!
   

2. Number:

   let count = 42;
   console.log(count); // Output: 42
   

3. Boolean:

   let isActive = true;
   console.log(isActive); // Output: true
   

4. Undefined:

   let x;
   console.log(x); // Output: undefined
   

5. Null:

   let y = null;
   console.log(y); // Output: null
   

6. Symbol:

   let sym = Symbol('unique');
   console.log(sym); // Output: Symbol(unique)
   

1. Object:

   let person = {
       name: "Alice",
       age: 30
   };
   console.log(person); // Output: { name: 'Alice', age: 30 }
   

2. Array:

   let numbers = [1, 2, 3, 4, 5];
   console.log(numbers); // Output: [1, 2, 3, 4, 5]
   

JavaScript allows you to convert data from one type to another.

JavaScript automatically converts data types when necessary.

You can explicitly convert data types using functions like String(), Number(), and Boolean().

1. Declare a variable city using let and assign it the value "New York".
2. Declare a constant country and assign it the value "USA".
3. Print both variables to the console.

Solution:

1. Declare a variable score and assign it the value 100.
2. Convert the score to a string and store it in a new variable scoreStr.
3. Print the type of score and scoreStr to the console.

Solution:

1. Using var instead of let or const: Prefer let and const to avoid issues with hoisting and scope.
2. Reassigning const variables: Remember that const variables cannot be reassigned.
3. Type Coercion: Be mindful of implicit type conversion, which can lead to unexpected results.

In this section, we covered the basics of variables and data types in JavaScript. We learned how to declare variables using var, let, and const, and explored different data types and type conversion methods. Understanding these concepts is essential for writing effective JavaScript code. In the next section, we will delve into basic operators and how to use them in JavaScript.