Help in Javascript question

let differnce = 0;
let currentNum;
let previousNum;
while(currentNum !== 999) {
    currentNum = parseInt(prompt("Enter a number"));
    if(!previousNum) {
        previousNum = currentNum;
    }
    console.log("current num: ", currentNum);
    console.log("previous num: " , previousNum);
    differnece = currentNum - previousNum;
    if(currentNum % 3 === 0) {
        console.log(`${currentNum} can be divided by 3`);
    }
    else if(differnce > 10) {
        console.log(`${currentNum} is much higher than the previous num: ${previousNum}`);
    } else {
        console.log("none of the condiots have been met");
    }
    previousNum = currentNum;
}