Here the code, note that "addEventListener" works only from IE9, if you need also support of earlier IE, just change "addEventListener" to the "onkeydown" event.
var handleBackSpace = function handleBackSpaceFunction(evt) {
switch (evt.target.tagName.toLowerCase()) {
case "input":
if (evt.target.type.toLowerCase() == "text" || evt.target.type.toLowerCase() == "password") {
disableIfNeeded(evt);
break;
//case of checkboxes
} else {
evt.preventDefault();
}
case "textarea":
disableIfNeeded(evt)
break;
default:
disableBackspace(evt)
break;
}
}
document.addEventListener('keydown', handleBackSpace, false);
function disableIfNeeded(evt) {
if (evt.target.readOnly == true) {
evt.preventDefault();
}
}
function disableBackspace(evt) {
var key;
if (typeof evt.keyIdentifier !== "undefined") {
key = evt.keyIdentifier;
} else if (typeof evt.keyCode !== "undefined") {
key = evt.keyCode;
}
if (key === 'U+0008' ||
key === 'Backspace' ||
key === 8) {
evt.preventDefault();
}
}