check if on screen javascript code example

Example 1: javascript detect touch screen

function isTouchScreendevice() {
    return 'ontouchstart' in window || navigator.maxTouchPoints;      
};

if(isTouchScreendevice()){
    alert("I am a touch screen device")
}

Example 2: if mousepressed javascript

var mouseDown = 0;
document.body.onmousedown = function() { 
  ++mouseDown;
}
document.body.onmouseup = function() {
  --mouseDown;
}