Basic if...else Statement

This snippet demonstrates the fundamental usage of the if...else statement in JavaScript, enabling conditional code execution based on a boolean expression.

Core Concept: Conditional Execution

The if...else statement allows you to execute different blocks of code depending on whether a specified condition is true or false. The if block executes if the condition evaluates to true. The else block (optional) executes if the condition evaluates to false.

Code Example

This code checks if the age variable is greater than or equal to 18. If it is, the message "You are eligible to vote." is printed to the console. Otherwise, the message "You are not eligible to vote yet." is printed.

let age = 20;

if (age >= 18) {
  console.log("You are eligible to vote.");
} else {
  console.log("You are not eligible to vote yet.");
}

Explanation of the Code

1. We declare a variable named age and assign it the value 20. 2. The if statement checks if age >= 18. This expression evaluates to true because 20 is greater than or equal to 18. 3. Since the condition is true, the code inside the if block is executed, printing "You are eligible to vote." to the console. 4. If age were less than 18, the code inside the else block would be executed instead.

Real-Life Use Case

if...else statements are commonly used for validating user input, determining access rights, displaying different content based on user roles, handling error conditions, and implementing game logic.

Best Practices

• Keep the conditions in if statements simple and easy to understand.
• Use meaningful variable names to improve readability.
• Use braces {} even for single-line blocks to avoid confusion.
• Consider using a switch statement when dealing with multiple conditions based on the same variable.
• Avoid deeply nested if...else statements as they can become difficult to maintain.

Interview Tip

Be prepared to explain the purpose of if...else statements, provide examples of their use, and discuss best practices for writing clear and maintainable conditional code. Understand the difference between if...else and switch statements.

When to use them

Use if...else statements when you need to execute different code blocks based on a condition that can be evaluated as either true or false. They are especially useful for handling binary decisions or branching logic.

Memory footprint

The memory footprint of if...else statements is minimal. They only consume a small amount of memory to store the condition and the pointers to the code blocks to be executed. The impact on overall performance is negligible unless used excessively in computationally intensive operations.

Alternatives

Alternatives to if...else statements include:

• Ternary operator: A concise way to write simple conditional expressions.
• Switch statement: Useful for handling multiple conditions based on the same variable.
• Lookup tables (objects or maps): Can be used to map input values to corresponding actions or results.
• Strategy pattern: Encapsulates different algorithms or behaviors into separate classes, allowing you to choose the appropriate strategy at runtime.

Pros

• Simple and easy to understand.
• Allows for conditional code execution based on boolean expressions.
• Provides flexibility in handling different scenarios.

Cons

• Can become complex and difficult to maintain with deeply nested conditions.
• May not be the most efficient solution for handling multiple conditions based on the same variable (consider using a switch statement instead).