JavaScript Control Flow Statements

Control flow statements in JavaScript control the order in which code is executed. These statements allow you to make decisions, repeat tasks, and jump between parts of a program based on specific conditions.

JavaScript if Statement

The if statement executes a block of code only if a specified condition is true.

const age = 18;
if (age >= 18) {
    console.log("You are an adult.");
}

You are an adult.

• Checks if age is greater than or equal to 18.
• Logs "You are an adult." if the condition is true.

JavaScript if...else Statement

The if...else statement provides an alternate block of code to execute if the condition is false.

const score = 40;
if (score >= 50) {
    console.log("You passed.");
} else {
    console.log("You failed.");
}

You failed.

• It will log "You passed." if the score is 50 or more.
• Otherwise, logs "You failed."

JavaScript if...else if...else Statement

The if...else if...else statement is used when you want to handle multiple conditions.

const temp = 25;
if (temp > 30) {
    console.log("It's hot.");
} else if (temp >= 20) {
    console.log("It's warm.");
} else {
    console.log("It's cold.");
}

It's warm.

• Checks if the temperature is greater than 30, logs "It's hot."
• If not, checks if it's between 20 and 30, logs "It's warm."
• Otherwise, logs "It's cold."

JavaScript switch Statement

The switch statement evaluates an expression and executes a block of code based on matching cases. It provides an alternative to long if-else chain.

const day = "Monday";
switch (day) {
    case "Monday":
        console.log("Start of the week.");
        break;
    case "Friday":
        console.log("End of the workweek.");
        break;
    default:
        console.log("It's a regular day.");
}

Start of the week.

• Checks the value of day and matches it to a case.
• Logs "Start of the week." if day is "Monday".
• Logs "End of the workweek." if day is "Friday".
• Logs "It's a regular day." if no cases match.

JavaScript Ternary Operator or Conditional Operator:

In some programming languages, a ternary operator is used to assign a value to a variable based on a condition.

let a = 10;
console.log(a === 5 ? "a is equal to 5" : "a is not equal to 5");

Output

a is not equal to 5

• Variable Declaration: let a = 10; assigns 10 to variable a.
• Ternary Operator: a === 5 ? "a is equal to 5" : "a is not equal to 5"; checks if a is strictly equal to 5.
  • If true, it returns "a is equal to 5".
  • If false, it returns "a is not equal to 5".

Uses of Control Flow Statements

Control flow statements are backbone in programming for

• Decision-Making: To execute specific blocks of code based on conditions (e.g., if, if...else).
• Branching: To exit loops or skip iterations (break, continue).
• Looping: To repeat tasks (for, while, do...while).
• Switching: To handle multiple conditions effectively (switch).

Suggested Quiz

6 Questions

What does the if statement do in programming?

• A
  It executes a block of code only if a specified condition is false.
• B
  It executes a block of code only if a specified condition is true.
• C
  It executes a block of code regardless of any conditions.
• D
  It executes multiple blocks of code simultaneously.

Explanation:

In JavaScript, which statement is used to handle multiple conditions?

• A
  if statement
• B
  for loop
• C
  switch statement
• D
  while loop

Explanation:

What is the purpose of the else clause in an if...else statement?

• A
  To provide an alternative block of code if the condition is true.
• B
  To provide an alternative block of code if the condition is false.
• C
  To execute the same block of code as the if statement.
• D
  To terminate the program if the condition is false.

Explanation:

Which of the following statements best describes the use of the ternary operator?

• A
  It is used to perform loops in JavaScript.
• B
  It is used to simplify if...else statements into a single line.
• C
  It is used to define functions in JavaScript.
• D
  It is used to declare variables in JavaScript.

Explanation:

What is the primary function of a switch statement in programming?

• A
  To repeat a block of code multiple times.
• B
  To execute code based on a single condition.
• C
  To evaluate an expression and execute code based on matching cases.
• D
  To define the main function of a program.

Explanation:

What happens if no cases match in a switch statement?

• A
  The program will throw an error.
• B
  The default case will execute if defined.
• C
  The switch statement will terminate immediately.
• D
  The program will skip to the next statement outside the switch.

Explanation:

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