Are certain keydown-event combinations blocking each other?

Question

I have a beginner's question on JavaScript: In a small testing script I oberserved that some key-events seemingly do not trigger when others are already triggered. In other words: If some keys are down, most of the other keydown-events are kind of blocked. For example holding down keys a, s, d, f, g do not trigger the keydown-event for g. However, If I am holding e.g. h and j down, too, their keydown-event is triggered as expected.

For this test I've used Mozilla Firefox 26.0 on Windows 7 Home Edition 64-Bit.

Here is the included JavaScript file which is used to output the map of key-events with keydown-type to some div-element with id "testout001":

var keyMap = [];

function keyMapToHTML(arr){
    var i = 0;
    var temp = "";
    while(i<arr.length){
        if(arr[i]){
            temp += i + "<br>";
        }
        i++;
    }
    return temp;
}

function keyHandler(e){
    e = e || event; // deal with IE
    keyMap[e.keyCode] = (e.type == 'keydown');
    document.getElementById("testout001").innerHTML = keyMapToHTML(keyMap);
}

First of all: Is this a bug?
Why are certain keydown-combinations working while others won't?
Are there limits (most likely browser-specific) to how many keys can be hold down/pressed at the same time?

Thank you in advance for your suggestions!

Jusso Jusso · Accepted Answer · 2014-01-13T13:25:24

It's a common hardware issue with most keyboards. Certain keypresses just cannot be detected at the same time.

Are certain keydown-event combinations blocking each other?

1 Answers