[javascript] Check if an element is a child of a parent

In addition to the other answers, you can use this less-known method to grab elements of a certain parent like so,

$('child', 'parent');

In your case, that would be

if ($(event.target, 'div#hello')[0]) console.log(`${event.target.tagName} is an offspring of div#hello`);

Note the use of commas between the child and parent and their separate quotation marks. If they were surrounded by the same quotes

$('child, parent');

you'd have an object containing both objects, regardless of whether they exist in their document trees.