Issue with javascript onkeydown - event.which give

问题:

I have written a piece of javascript code to get the key pressed within a text area. I have used the onkeydown event to capture the key pressed and am calling a function when the event is triggered. Within the function i am using event.which to get the key pressed. But this is not giving the correct key pressed. For any character pressed, it gives the Ascii value of the corresponding upper case character ( 65 to 90 only ). It is not giving Ascii values for the lower case characters, ie 97 to 122, even if a lower case character has been typed. Eg - If i type 'a' it gives the Ascii value of 'A' Does any one know why this is happening ? Here is the code i am using -

var mainDoc = document.getElementById("mainDoc");
mainDoc.onkeydown = function(event){keyPress(event);}
function keyPress(event)
{
    alert("key code : "+ event.which + " );
}

I tried using onkeypress event. This seems to work fine, but it does not capture the alt, control, arrow keys etc.

回答1:

keydown and keyup don't (mostly) give you characters at all, they give you keycodes. keypress is where you get characters (and if you need to know, also the state of the modifier keys as of when that character was typed, on the event object's ctrlKey, altKey, shiftKey, and metaKey properties). This page goes into the madness that is keyboard events in JavaScript in loving detail...

回答2:

The issue is that keydown event will report keypresses - that is, physical keys pressed. The keypress event will report the translated keys, meaning the character that has been derived from the keys pressed (Shift + a == A). In order to get the actual keys, you may need to keep track of both keydown/keyup (to monitor the modifier keys) and keypress (to monitor the actual alphanumeric user input.)

回答3:

From http://www.bloggingdeveloper.com/post/KeyPress-KeyDown-KeyUp-The-Difference-Between-Javascript-Key-Events.aspx

In order to understand the difference between keydown and keypress, it is useful to understand the difference between a "character" and a "key". A "key" is a physical button on the computer's keyboard while a "character" is a symbol typed by pressing a button. In theory, the keydown and keyup events represent keys being pressed or released, while the keypress event represents a character being typed. The implementation of the theory is not same in all browsers.

回答4:

function getKeyCode(event) {
   event = event || window.event;
   return event.keyCode;
}

use event.keyCode will give u the keycode ;)

g.r.