JavaScript Conditional Statements

Conditional statements allow a program to make decisions and execute different blocks of code based on conditions.

---

1. if Statement

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

Syntax

if (condition) {
  // code to execute
}

Example

let age = 20;

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

Flowchart

     Start
       |
       v
   Condition?
    /      \
 True      False
   |          |
   v          |
 Execute      |
 Code         |
   |          |
   v          |
     End <----

When to Use

• When you want to execute code only if a condition is true.
• No action is needed when the condition is false.

---

2. if...else Statement

The if...else statement provides two possible execution paths.

Syntax

if (condition) {
  // code if true
} else {
  // code if false
}

Example

let age = 16;

if (age >= 18) {
  console.log("Eligible to vote");
} else {
  console.log("Not eligible to vote");
}

Flowchart

       Start
         |
         v
     Condition?
      /      \
   True      False
    |           |
    v           v
 Execute A   Execute B
    |           |
    +-----+-----+
          |
          v
         End

When to Use

• When there are exactly two possible outcomes.
• Example: Pass/Fail, Yes/No, Adult/Minor.

---

3. else if Statement

Used when multiple conditions need to be checked.

Syntax

if (condition1) {
  // code
} else if (condition2) {
  // code
} else {
  // code
}

Example

let marks = 78;

if (marks >= 90) {
  console.log("Grade A");
} else if (marks >= 75) {
  console.log("Grade B");
} else if (marks >= 50) {
  console.log("Grade C");
} else {
  console.log("Fail");
}

Flowchart

          Start
            |
            v
      Condition 1?
        /      \
     Yes       No
      |         |
      v         v
  Execute A  Condition 2?
               /    \
            Yes      No
             |        |
             v        v
        Execute B  Condition 3?
                     /     \
                  Yes      No
                   |        |
                   v        v
             Execute C  Execute D
                   |        |
                   +----+---+
                        |
                        v
                       End

When to Use

• When multiple conditions need to be evaluated.
• Example: Grades, Salary Ranges, User Roles.

---

4. switch Statement

The switch statement compares a single value against multiple cases.

Syntax

switch (expression) {
  case value1:
    // code
    break;

  case value2:
    // code
    break;

  default:
    // code
}

Example

let day = 3;

switch (day) {
  case 1:
    console.log("Monday");
    break;

  case 2:
    console.log("Tuesday");
    break;

  case 3:
    console.log("Wednesday");
    break;

  default:
    console.log("Invalid Day");
}

Flowchart

          Start
            |
            v
      Check Value
            |
    +---+---+---+
    |   |   |   |
 Case1 Case2 Case3
    |   |   |   |
    v   v   v   v
 Code Code Code Default
    |   |   |   |
    +---+---+---+
            |
            v
           End

When to Use

• When comparing the same variable against multiple values.
• Cleaner than many else if statements.

---

5. Ternary Operator (?:)

A shorthand version of if...else.

Syntax

condition ? valueIfTrue : valueIfFalse;

Example

let age = 20;

let result = age >= 18
  ? "Adult"
  : "Minor";

console.log(result);

Flowchart

       Start
         |
         v
     Condition?
      /      \
   True      False
    |           |
    v           v
 Value A     Value B
      \       /
       \     /
        \   /
         \ /
          v
         End

When to Use

• For simple conditions.
• Avoid for complex nested logic.

---

Summary Table

Conditional Statement	Purpose
if	Execute code when a condition is true
if...else	Choose between two outcomes
else if	Handle multiple conditions
switch	Compare one value against multiple cases
Ternary (?:)	Short form of if...else

Key Takeaway

• Use if for a single condition.
• Use if...else for two outcomes.
• Use if...else if...else for multiple conditions.
• Use switch when checking many values of the same variable.
• Use the ternary operator for concise one-line decisions.

References:
https://www.geeksforgeeks.org/javascript/conditional-statements-in-javascript/
https://www.w3schools.com/js/js_conditionals.asp