Select elements by attribute
Solution 1:
if ($('#A').attr('myattr')) {
// attribute exists
} else {
// attribute does not exist
}
EDIT:
The above will fall into the else-branch when myattr exists but is an empty string or "0". If that's a problem you should explicitly test on undefined:
if ($('#A').attr('myattr') !== undefined) {
// attribute exists
} else {
// attribute does not exist
}
Solution 2:
Do you mean can you select them? If so, then yes:
$(":checkbox[myattr]")