Growing Reverse Number Pattern in JavaScript

What You’ll Learn

Program 61 prints a growing reverse-number pattern: starting from an integer like 86523, build the reverse one digit at a time and print each partial result — 3, 32, 325, and so on. This tutorial covers modulo, reverse building, a live preview, worked JavaScript examples, edge cases, and O(d) complexity.

📝 Problem & Approach

Given starting integer num = 86523, build its reverse one digit at a time and print each partial reverse until all digits are processed.

// num = 86523
//3
//32
//325
//3256
//32568

Inputs & Outputs

Minimal workflow

reverse = 0
while num is not 0:
    digit = num % 10
    reverse = reverse * 10 + digit
    log reverse
    num = floor(num / 10)

Approach comparison

🔮 Live Preview

Enter a positive integer between 10 and 99999999 and draw the growing reverse pattern in the browser.

Press "Draw pattern".

Examples Gallery

Three complete JavaScript programs — fixed starting value, user input with abs, and a compact num = 123 trace. Click View Output to reveal sample console results.

let num = 86523;
let reverse = 0;

while (num !== 0) {
  reverse = reverse * 10;
  reverse = reverse + (num % 10);
  console.log(reverse);
  num = Math.floor(num / 10);
}

3
32
325
3256
32568

const numInput = prompt("Enter a number:");
const parsed = parseInt(numInput, 10);

if (!Number.isFinite(parsed)) {
  console.log("Please enter a valid integer.");
} else {
  let num = Math.abs(parsed);
  let reverse = 0;

  while (num !== 0) {
    reverse = reverse * 10 + (num % 10);
    console.log(reverse);
    num = Math.floor(num / 10);
  }
}

Enter a number: 86523
3
32
325
3256
32568

let num = 123;
let reverse = 0;

while (num !== 0) {
  reverse = reverse * 10 + (num % 10);
  console.log(reverse);
  num = Math.floor(num / 10);
}

3
32
321

🔎 Worked Walkthrough — num = 86523

Trace each loop iteration: extract the digit, update reverse, log, then shrink num.

Total lines logged: 5 = digit count of the starting number. Final reverse equals the full reversed number.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices