TypeScript code to check if the given number is present in the Fibonacci series

index.ts

function isPerfectSquare(n: number) : boolean {
    return n > 0 && Math.sqrt(n) % 1 === 0;
}

function isFibonacci(input: number) : boolean {
    return isPerfectSquare(5*input*input + 4) || isPerfectSquare(5*input*input - 4)
}

console.log(isFibonacci(4))
console.log(isFibonacci(8))
console.log(isFibonacci(1))
console.log(isFibonacci(41))

Output :

false
true
true
false