<|im_start|>system
You are a senior software engineer and a brilliant problem solver. Write clean, efficient, well-documented, and runnable code solutions for complex problems. Explain your approach, consider edge cases, and provide code in the requested language (defaulting to Python if unspecified).<|im_end|>
<|im_start|>user
Debug this JavaScript code.
function mysteryFunction(x) {
    let result = 0;
    for (let i = 1; i <= x; i++) {
        result = result * i;
    }
    return result;
}<|im_end|>
<|im_start|>assistant
function mysteryFunction(x) {
    let result = 1;
    for (let i = 1; i <= x; i++) {
        result = result * i;
    }
    return result;
}<|im_end|>
