Which of the following is true?
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If onKeyDown returns false, the key-press event is cancelled
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If onKeyPress returns false, the key-down event is cancelled.
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If onKeyDown returns false, the key-up event is cancelled.
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If onKeyPress returns false, the key-up event is canceled.
Returning false from a key event handler like onKeyDown cancels the default browser action of that key press, effectively cancelling the keypress event. The keyup event will still fire, and keydown itself has already occurred, so other options are incorrect.
To answer this question, we need to understand the difference between the key-down, key-press, and key-up events in JavaScript.
The key-down event is triggered when a key on the keyboard is pressed down. The key-press event is triggered when a key is pressed and released. The key-up event is triggered when a key is released.
Now let's go through each option to understand why it is correct or incorrect:
Option A) If onKeyDown returns false, the key-press event is cancelled. This option is incorrect. The onKeyDown event does not cancel the key-press event. The onKeyDown event is triggered before the key-press event and can be used to prevent the default behavior of the key-press event, but it does not cancel it.
Option B) If onKeyPress returns false, the key-down event is cancelled. This option is incorrect. The onKeyPress event does not cancel the key-down event. The onKeyPress event is triggered after the key-down event and can be used to prevent the default behavior of the key-down event, but it does not cancel it.
Option C) If onKeyDown returns false, the key-up event is cancelled. This option is incorrect. The onKeyDown event does not cancel the key-up event. The onKeyDown event is triggered before the key-up event and can be used to prevent the default behavior of the key-up event, but it does not cancel it.
Option D) If onKeyPress returns false, the key-up event is canceled. This option is incorrect. The onKeyPress event does not cancel the key-up event. The onKeyPress event is triggered after the key-up event and can be used to prevent the default behavior of the key-up event, but it does not cancel it.
Therefore, the correct answer is A) If onKeyDown returns false, the key-press event is cancelled. This option is correct because returning false from the onKeyDown event will prevent the key-press event from being triggered.