Conditional Statements in JavaScript

Conditional statements in JavaScript allow developers to control the flow of code by executing different blocks of code based on specific conditions. The main types of conditional statements are if, else, else if, and switch. This article explains each type with examples.

1. if Statement

The if statement executes a block of code if the specified condition evaluates to true. This is the most basic conditional statement.

Example: Using an if statement

      let age = 18;
      if (age >= 18) {
        console.log("You are eligible to vote.");
      }
      // Output: You are eligible to vote.
    

2. if-else Statement

The if-else statement allows code to be executed if the condition is true, and a different block of code if the condition is false.

Example: Using an if-else statement

      let age = 16;
      if (age >= 18) {
        console.log("You are eligible to vote.");
      } else {
        console.log("You are not eligible to vote.");
      }
      // Output: You are not eligible to vote.
    

3. if-else if-else Statement

The if-else if-else statement allows for multiple conditions to be checked sequentially. It executes the first block of code where the condition is true. If none of the conditions are met, the else block is executed.

Example: Using an if-else if-else statement

      let score = 85;

      if (score >= 90) {
        console.log("Grade: A");
      } else if (score >= 80) {
        console.log("Grade: B");
      } else if (score >= 70) {
        console.log("Grade: C");
      } else {
        console.log("Grade: F");
      }
      // Output: Grade: B
    

4. Nested if Statements

if statements can be nested within each other to create more complex conditions. This is helpful when you have multiple layers of conditions.

Example: Using nested if statements

      let age = 20;
      let hasID = true;

      if (age >= 18) {
        if (hasID) {
          console.log("You are allowed to enter.");
        } else {
          console.log("ID required to enter.");
        }
      } else {
        console.log("You are too young to enter.");
      }
      // Output: You are allowed to enter.
    

5. switch Statement

The switch statement is useful when you need to compare a single expression with multiple potential values. Each case represents a value, and default is executed if no cases match.

Example: Using a switch statement

      let day = 3;
      let dayName;

      switch (day) {
        case 1:
          dayName = "Monday";
          break;
        case 2:
          dayName = "Tuesday";
          break;
        case 3:
          dayName = "Wednesday";
          break;
        case 4:
          dayName = "Thursday";
          break;
        case 5:
          dayName = "Friday";
          break;
        default:
          dayName = "Invalid day";
      }
      console.log(dayName);  // Output: Wednesday
    

The switch statement can be more readable than multiple if-else statements when checking a single expression against several values.

6. Ternary Operator

The ternary operator (condition ? expressionIfTrue : expressionIfFalse) is a shorthand for simple if-else statements. It returns one of two values based on the condition.

Example: Using the ternary operator

      let age = 18;
      let accessMessage = age >= 18 ? "Access granted" : "Access denied";
      console.log(accessMessage);  // Output: Access granted
    

The ternary operator is a concise way to write conditional statements, especially for assignments or simple logic.

Summary of Conditional Statements

• if: Executes a block if the condition is true.
• if-else: Executes one block if the condition is true, another if false.
• if-else if-else: Checks multiple conditions sequentially.
• Nested if: Places if statements within each other for complex conditions.
• switch: Compares a single expression with multiple values, often for simpler, cleaner code.
• Ternary operator: A shorthand for simple if-else statements.

Conclusion

Conditional statements are essential for controlling the flow of a program. They allow developers to create logic that responds to different conditions and inputs, making applications interactive and dynamic. Understanding the various conditional statements in JavaScript helps in writing efficient and readable code.