Raw code:

function printNaturalNumbers() {
    n = Number(prompt("Enter a number: "))
    if (isNaN(n) || n < 1) {
        console.log("Wrong input, try again.")
    } else {
        ans = ""
        for (let i = 1; i < n + 1; i++) {
            ans += `${i} `
        }
        console.log(ans)
    }
}

function printNto1() {
    n = Number(prompt("Enter a number: "))
    if (isNaN(n) || n < 1) {
        console.log("Wrong input, try again.")
    } else {
        ans = ""
        for (let i = n; i > 0; i--) {
            ans += `${i} `
        }
        console.log(ans)
    }
}

function sumUpToN() {
    n = Number(prompt("Enter a number: "))
    if (isNaN(n) || n < 1) {
        console.log("Wrong input, try again.")
    } else {
        let sum = 0
        for (let i = 1; i <= n; i++) {
            sum += i
        }
        console.log(sum)
    }
}

function factorial() {
    n = Number(prompt("Enter a number: "))
    if (isNaN(n) || n < 1) {
        console.log("Wrong input, try again.")
    } else {
        let fact = 1
        for (let i = 1; i <= n; i++) {
            fact *= i
        }
        console.log(fact)
    }
}

function sumEvenOddInRange() {
    start = Number(prompt("Enter start: "))
    end = Number(prompt("Enter end: "))

    if (isNaN(start) || isNaN(end)) {
        console.log("Wrong input, try again.")
    } else {
        if (start > end) {
            [start, end] = [end, start];
        }
        let evenSum = 0, oddSum = 0
        for (let i = start; i <= end; i++) {
            i % 2 === 0 ? evenSum += i : oddSum += i
        }
        console.log("Sum of even numbers in the range and 
        Sum of odd numbers in the range are " + [evenSum, oddSum])
    }
}

function printFactors() {
    n = Number(prompt("Enter a number: "))
    if (isNaN(n) || n < 1) {
        console.log("Wrong input, try again.")
    } else {
        let str = ""
        for (let i = 0; i < n + 1; i++) {
            if (n % i == 0) str += `${i} `
        }
        console.log(str)
    }
}

function isPrime() {
    n = Number(prompt("Enter a number: "))
    if (isNaN(n)) {
        console.log("Wrong input, try again.")
    } else {
        if(n==2){
            console.log("Prime")
        }
        else if(n<=1||n%2==0){
            console.log("Not Prime")
        }
        else{
            for(let i=3;i<n;i++){
                if(n%i==0){
                    return console.log("Not Prime")
                }
            }
            console.log("Prime")
        }
    }
}

function calculatePower() {
    a = Number(prompt("Enter a number: "))
    b = Number(prompt("Enter the exponent: "))

    if (isNaN(a) || isNaN(b)) {
        console.log("Wrong input, try again.")
    } else {
        let ans = 1;
        let exp = Math.abs(b);

        for (var i = 0; i < exp; i++) {
            ans *= a;
        }
        let result = b >= 0 ? ans : 1 / ans
        console.log(`${a} to the power ${b} is ${result}`) 
    }
}
            

Optimized code

function getNumberInput(message) {
    let n = Number(prompt(message));
    return isNaN(n) || n < 1 ? null : n;
}

function printNaturalNumbers() {
    let n = getNumberInput("Enter a number:");
    if (!n) return console.log("Wrong input, try again.");
    console.log([...Array(n).keys()].map(i => i + 1).join(" "));
}

function printNto1() {
    let n = getNumberInput("Enter a number:");
    if (!n) return console.log("Wrong input, try again.");
    console.log([...Array(n).keys()].map(i => n - i).join(" "));
}

function sumUpToN() {
    let n = getNumberInput("Enter a number:");
    if (!n) return console.log("Wrong input, try again.");
    console.log((n * (n + 1)) / 2); // Using formula for efficiency
}

function factorial() {
    let n = getNumberInput("Enter a number:");
    if (!n) return console.log("Wrong input, try again.");
    console.log([...Array(n).keys()].map(i => i + 1).reduce((a, b) => a * b, 1));
}

function sumEvenOddInRange() {
    let start = Number(prompt("Enter start:"));
    let end = Number(prompt("Enter end:"));

    if (isNaN(start) || isNaN(end)) return console.log("Wrong input, try again.");
    if (start > end) [start, end] = [end, start];

    let evenSum = 0, oddSum = 0;
    for (let i = start; i <= end; i++) i % 2 === 0 ? evenSum += i : oddSum += i;

    console.log(`Sum of evens: ${evenSum}, Sum of odds: ${oddSum}`);
}

function printFactors() {
    let n = getNumberInput("Enter a number:");
    if (!n) return console.log("Wrong input, try again.");
    console.log([...Array(n + 1).keys()].filter(i => i && n % i === 0).join(" "));
}

function isPrime() {
    let n = getNumberInput("Enter a number:");
    if (!n) return console.log("Wrong input, try again.");
    if (n < 2) return console.log("Not Prime");
    if (n === 2 || n === 3) return console.log("Prime");
    if (n % 2 === 0 || n % 3 === 0) return console.log("Not Prime");

    for (let i = 5; i * i <= n; i += 6)
        if (n % i === 0 || n % (i + 2) === 0) return console.log("Not Prime");

    console.log("Prime");
}

function calculatePower() {
    let a = Number(prompt("Enter a number:"));
    let b = Number(prompt("Enter the exponent:"));

    if (isNaN(a) || isNaN(b)) return console.log("Wrong input, try again.");
    console.log(`${a} to the power ${b} is ${b >= 0 ? a ** b : 1 / (a ** -b)}`);
}