Timer in a local scope variable in javascript

The timer must be initialized and the seconds have to be incremented each second. Can someone help me? I am not sure what is going on.

function timer(){
    let seconds = "00";
    let minutes = "00";
    let hours = "00";
    let fulltime = `${hours}:${minutes}:${seconds}`;

    const incrementSeconds = () => {
        secondsAsNumber = parseInt(seconds) + 1;
        seconds = secondsAsNumber.toString();
    }
    
    const displayTime = () => {
        console.log(fulltime);
    }
    
    setInterval(() => {
        incrementSeconds();
        displayTime();
    }, 1000);
}

timer();

It logs:

00:00:00
00:00:00
00:00:00
00:00:00
00:00:00
00:00:00
00:00:00

>Solution :

Update your fulltime variable after incrementing seconds:

function timer(){
    let seconds = "00";
    let minutes = "00";
    let hours = "00";
    let fulltime = `${hours}:${minutes}:${seconds}`;

    const incrementSeconds = () => {
        secondsAsNumber = parseInt(seconds) + 1;
        seconds = secondsAsNumber.toString();
        // Update fulltime variable
        fulltime = `${hours}:${minutes}:${seconds < 10 ? "0" + seconds : seconds}`;
    }
    
    const displayTime = () => {
        console.log(fulltime);
    }
    
    setInterval(() => {
        incrementSeconds();
        displayTime();
    }, 1000);
}

timer();

Then it should output:

00:00:01
00:00:02
00:00:03
00:00:04
00:00:05

... and so on ...