Refreshing Javascript Timer

I'm trying to making an correct/wrong application using javascript. This is my timer code:

var timeleft = 3;
var downloadTimer = setInterval(function() {
    timeleft--;
    document.getElementById("geri_sayim").textContent = timeleft;
    if (timeleft <= 0) {
        clearInterval(downloadTimer);
        alert("time is up");
    }
},1000);

I have these functions:

CreateQuestion();
CheckAnswer();
isConfirm();

When I add this timer into CreateQuestion(), it works. But I want to stop this timer when the user clicks an answer button. For this reason I add this code into CheckAnswer()

clearInterval(downloadTimer);

But when I do this, the application doesn't work, and neither does the timer. Basically I want to countdown from 3 for each question. What's my mistake?

Solution

This solution works for what you want to achieve:

HTML

<body onload="createQuestion();">
<p id="my-question"></p>
<p id="time-left">3</p>
<button onclick="checkAnswer();">Check Answer</button>

JavaScript

var timeleft = 3;
var myTimer;

function createQuestion() {
    // You create your question..
    document.getElementById("my-question").innerHTML = "Do you know the answer to this question?";
    // ..and start the timer..
    myTimer = setInterval(function() {
    timeleft--;
    document.getElementById("time-left").textContent = timeleft;
    if (timeleft <= 0) {
        clearInterval(myTimer);
        alert("Time is up!");
    }
    },1000);
}
function checkAnswer() {
    // Pause the time!
    clearInterval(myTimer);
    alert("Time paused!");
}
function isConfirm() {
    // Whatever other code you wrote for this function
}