The easiest way to do that is to set a flag variable and console.log the result if the flag is true. something like that:

    var flag = true;
    function onScanSuccess(decodedText, decodedResult) {
        if(flag){
            console.log(`Code scanned = ${decodedText}`, decodedResult);
            flag = false;
        }
    }

    setInterval(()=>flag=true, 1000);

    var html5QrcodeScanner = new Html5QrcodeScanner(
        "qr-reader", { fps: 10, qrbox: 250 });
    html5QrcodeScanner.render(onScanSuccess);

There's another way too. we can change the flag with setTimeout in the onScanSuccess function.

    var flag = true;
    function onScanSuccess(decodedText, decodedResult) {
        if(flag){
            console.log(`Code scanned = ${decodedText}`, decodedResult);
            flag = false;
            setTimeout(()=>flag=true, 1000);
        }
    }

    var html5QrcodeScanner = new Html5QrcodeScanner(
        "qr-reader", { fps: 10, qrbox: 250 });
    html5QrcodeScanner.render(onScanSuccess);

First of all, thanks for all the answers and comments.

In the end it worked with the tweaking of the fps. I changed the fps: 10 to fps: 1. Thanks @nicael for that answer.

var html5QrcodeScanner = new Html5QrcodeScanner(
    "qr-reader", { fps: 1, qrbox: 250 });
html5QrcodeScanner.render(onScanSuccess);

If you searched for an answer to disable a function for a specific time, look at @Alireza Jahandoost answer that one's perfect for that case.