How to clear a textbox using javascript

Question

I have a

I need a javascript method to clear the value of the textbox when the focus is

Answer 1

For my coffeescript peeps!

#disable Delete button until reason is entered
$("#delete_event_button").prop("disabled", true)
$('#event_reason_is_deleted').click ->
    $('#event_reason_is_deleted').val('')
    $("#delete_event_button").prop("disabled", false)