Check for perfect square in JavaScript

We are required to write a JavaScript function that takes in a number and returns a boolean based on the fact whether or not the number is a perfect square.

A perfect square is a number that can be expressed as the product of an integer with itself. For example, 16 is a perfect square because 4 × 4 = 16.

Examples of Perfect Square Numbers

144 (12²), 196 (14²), 121 (11²), 81 (9²), 484 (22²)

Method 1: Using Math.sqrt()

The most straightforward approach is to find the square root and check if it's an integer:

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

console.log(isPerfectSquare(484));  // true
console.log(isPerfectSquare(485));  // false
console.log(isPerfectSquare(121));  // true
console.log(isPerfectSquare(0));    // true

true
false
true
true

Method 2: Using Loop Iteration

This approach iterates through numbers until we find a match or exceed the target:

const isPerfectSquareLoop = (num) => {
    if (num < 0) return false;
    
    let i = 1;
    while (i * i <= num) {
        if (i * i === num) {
            return true;
        }
        i++;
    }
    return false;
};

console.log(isPerfectSquareLoop(484));  // true
console.log(isPerfectSquareLoop(485));  // false
console.log(isPerfectSquareLoop(144));  // true

true
false
true

Method 3: Using Binary Search

For better performance with large numbers, binary search can be used:

const isPerfectSquareBinary = (num) => {
    if (num < 0) return false;
    if (num === 0) return true;
    
    let left = 1;
    let right = Math.floor(num / 2) + 1;
    
    while (left <= right) {
        const mid = Math.floor((left + right) / 2);
        const square = mid * mid;
        
        if (square === num) return true;
        if (square < num) left = mid + 1;
        else right = mid - 1;
    }
    return false;
};

console.log(isPerfectSquareBinary(484));  // true
console.log(isPerfectSquareBinary(500));  // false

true
false

Comparison

Conclusion

The Math.sqrt() method is the most efficient and readable approach for checking perfect squares. Use loop-based methods when you need to understand the underlying logic or avoid built-in math functions.