Dowhile in Javascript

Learn about dowhile in javascript with practical examples and code snippets.

Basic Do-While Loop

Code

const cars = [
  { id: 1, name: "Nexon", brand: "Tata", make: "2017", rating: 2 },
  { id: 2, name: "Verna", brand: "Hyundai", make: "2008", rating: 4 },
  { id: 3, name: "Bolero", brand: "Mahindra", make: "2012", rating: 5 },
  { id: 4, name: "Baleno", brand: "Maruti", make: "2022", rating: 4 },
  { id: 5, name: "Seltos", brand: "Kia", make: "2011", rating: 3 },
  { id: 6, name: "G-class", brand: "Mercedes", make: "2024", rating: 5 }
];
let i = 0;
do {
  console.log(`${cars[i].brand} -> ${cars[i].name}`);
  i++;
} while (i < cars.length);

Do-While Executes at Least Once

Output: Count: 0 Compare with while loop No output - doesn't execute.

Code

let count = 0;
do {
  console.log(`Count: ${count}`);
  count++;
} while (count < 0); // Condition is false, but still executes once
let count2 = 0;
while (count2 < 0) {
  console.log(`Count: ${count2}`);
  count2++;
}

Menu System (Common Use Case)

Display menu In real scenario: choice = getUserInput();.

Code

function showMenu() {
  let choice;
  do {
    console.log("1. Option 1");
    console.log("2. Option 2");
    console.log("3. Exit");
    choice = "3"; // Simulated
    if (choice === "1") {
      console.log("Executing option 1");
    } else if (choice === "2") {
      console.log("Executing option 2");
    }
  } while (choice !== "3");
  console.log("Exiting menu");
}

Input Validation

In real scenario: number = parseInt(prompt("Enter a number between 1-10:"));.

Code

function getValidNumber() {
  let number;
  do {
    number = 5; // Simulated
  } while (number < 1 || number > 10);
  return number;
}

Processing Until Condition

Output: Value: 10, 8, 6, 4, 2.

Code

let value = 10;
do {
  console.log(`Value: ${value}`);
  value -= 2;
} while (value > 0);

Retry Logic

success = tryOperation();.

Code

let attempts = 0;
let success = false;
const maxAttempts = 3;
do {
  attempts++;
  console.log(`Attempt ${attempts}`);
  success = attempts === 2; // Simulated
} while (!success && attempts < maxAttempts);
if (success) {
  console.log("Operation succeeded");
} else {
  console.log("Operation failed after max attempts");
}

Array Processing

When to Use Do-While ✅ Use when you need to execute code at least once ✅ Use for menu systems ✅ Use for input validation ✅ Use when condition depends on code execution ❌ Don't use when condition might be false initially and you don't want execution Use while loop instead in that case.

Code

let index = 0;
do {
  if (index < cars.length) {
    console.log(cars[index].name);
  }
  index++;
} while (index < cars.length);

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Summary

Understanding dowhile is essential for mastering javascript. Practice these examples and experiment with variations to deepen your understanding.

Key Takeaways

• dowhile is a fundamental concept in javascript
• Practice with these examples to build confidence
• Experiment with variations to explore edge cases
• Understanding dowhile will help you in technical interviews