I am currently developing a web application that requires me to detect if control is pressed.

I use keydown event to set a flag to true if the pressed key is ctrl then keyup event to set that flag to false. I'm using evt.ctrlKey to easily return true if the key pressed is the control key.

But to my surprise, I can see that evt.keyCode is equal to 17 while evt.ctrlKey gives me a false.

This does not happen to keydown event.

Please see this simple fiddle for reproduction. I'm using firefox 27.

PS : I know that I can just test if keyCode is 17 but I want to know if I missed something.

I am currently developing a web application that requires me to detect if control is pressed.

I use keydown event to set a flag to true if the pressed key is ctrl then keyup event to set that flag to false. I'm using evt.ctrlKey to easily return true if the key pressed is the control key.

But to my surprise, I can see that evt.keyCode is equal to 17 while evt.ctrlKey gives me a false.

This does not happen to keydown event.

Please see this simple fiddle for reproduction. I'm using firefox 27.

PS : I know that I can just test if keyCode is 17 but I want to know if I missed something.

• javascript
• jquery
• keyevent

• different events equal different keycodes indeed. – Alex Commented Feb 24, 2014 at 7:56
• Did you find anything unusual to my posted fiddle? Is my understanding wrong? – Bnrdo Commented Feb 24, 2014 at 7:58
• 2 its not wrong, the keyup did return false for the ctrlkey also. its just that different events have different states of the keys pressed. also, ctrlkey may be unreliable on different os – Alex Commented Feb 24, 2014 at 7:59
• What exactly is not right? You said it yourself I use keydown event to set a flag to true if the pressed key is ctrl then keyup event to set that flag to false but then you changed your mind about this being wrong? – Spokey Commented Feb 24, 2014 at 8:03
• To plicate things even more: I have a standard keyboard with two Ctrl keys. If you hold both down, and release one, you also get true on keyup check. This might explain more what @Good luck replied with "ctrl is pressed" at the time of the event. – thmshd Commented Feb 24, 2014 at 8:05

2 Answers 2

According to w3c docs ctrlKey event attribute returns true if it's presse and false if not, so your code is working right. On keydown event ctrl is pressed - so it returns keycode 17 and true , on keyup ctrl is not pressed, so the result is 17 and false.

The documentation for keyup says:

ctrlKey: true if the control key was down when the event was fired. false otherwise.

The keyup and keydown events are fired after the key has been pressed/released. So the state of ctrlKey is correctly down for the keydown event and up for the keyup event. More explicitly, the order is:

1. Press CTRL key.
2. Keydown event is fired.
3. Release CTRL key.
4. Keyup event is fired.

Furthermore, if you are looking for the CTRL key itself you should be checking the key code, not the ctrlKey property. The latter is for checking key binations, for example if you want CTRL+S, you would check for a keyup/keydown event of { keyCode: 83, ctrlKey: true }.