Check Perfect Square in JavaScript

What You’ll Learn

A perfect square equals k * k for some whole number k. Examples: 1, 4, 9, 16, 25. This tutorial covers the loop and Math.floor(Math.sqrt(n)) approaches, a live checker, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given an integer n, decide whether it is a perfect square of a non-negative integer.

# 16 -> 4 * 4 = 16   perfect
# 15 -> no integer k  not perfect
# 0  -> 0 * 0 = 0    perfect
# 1  -> 1 * 1 = 1    perfect

Inputs & Outputs

Minimal workflow

function isPerfectSquareLoop(n) {
  if (n < 0) {
    return false;
  }
  let i = 0;
  while (i * i <= n) {
    if (i * i === n) {
      return true;
    }
    i += 1;
  }
  return false;
}

Method comparison

🔮 Live Preview

Checks with integer logic, then reports the root and verdict.

Press “Run check” to see result.

Examples Gallery

Three complete JavaScript programs — loop check for 16, list squares from 1 to 50 with Math.sqrt, and generate squares by squaring. Click View Output to reveal sample console results.

function isPerfectSquare(number) {
  if (number < 0) {
    return false;
  }
  let i = 0;
  while (i * i <= number) {
    if (i * i === number) {
      return true;
    }
    i += 1;
  }
  return false;
}

const testNumber = 16;
if (isPerfectSquare(testNumber)) {
  console.log(`${testNumber} is a perfect square.`);
} else {
  console.log(`${testNumber} is not a perfect square.`);
}

16 is a perfect square.

function isPerfectSquare(num) {
  if (num < 0) {
    return false;
  }
  const root = Math.floor(Math.sqrt(num));
  return root * root === num;
}

console.log("Perfect Squares in the Range 1 to 50:");
let line = "";
for (let i = 1; i <= 50; i++) {
  if (isPerfectSquare(i)) {
    line += i + " ";
  }
}
console.log(line.trim());

Perfect Squares in the Range 1 to 50:
1 4 9 16 25 36 49 

console.log("First squares from k = 0 to 7:");
for (let k = 0; k <= 7; k++) {
  const square = k * k;
  console.log(`${k} * ${k} = ${square}`);
}

First squares from k = 0 to 7:
0 * 0 = 0
1 * 1 = 1
2 * 2 = 4
3 * 3 = 9
4 * 4 = 16
5 * 5 = 25
6 * 6 = 36
7 * 7 = 49

🔎 Worked Walkthrough — 16

Trace the loop method for n = 16.

4 * 4 equals 16 — perfect square.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

For interview demos, either method is fine; mention float pitfalls when asked about reliability.

💡 Best Practices