Develop Reference

How to disable Windows keys (logo key and menu key) using Javascript

I write this Javascript code but it doesn't disable 2 windows keys (I mean logo key and menu key), though:
document.onkeydown = function(e) {
document.title = e.keyCode;
if (e.keyCode == 91 || e.keyCode == 93) {
window.event.keyCode = 0;
window.event.returnValue = false;
return false;
}
};
the 2 window.xxx statements are actually not necessary but I add them in to buy an insurance (Just doubt that e doesn't totally equal to window.event).
So I'd like to ask this question: " Is there a feasible way, directly or indirectly, to do this job in Javascript? "

Your code looks right, try to find out real keycodes with this simple script:
document.onkeydown = checkKeycode
function checkKeycode(e) {
var keycode;
if (window.event) keycode = window.event.keyCode;
else if (e) keycode = e.which;
alert("keycode: " + keycode);
}
And to disabel certain keys you modify function (example for 'Enter'):
document.onkeydown = checkKeycode
function checkKeycode(e) {
var event = e || window.event;
var keycode = event.which || event.keyCode;
if (keycode == 13) {
// return key was pressed
}
}

JavaScript cannot stop the effect of the Windows logo key, which (when released) is supposed to bring up the Window's start menu. In combination with other keys, it has other system wide effects (like with M = minimise all windows). This is something that happens outside of the browser context, and thus cannot and should not be blocked by the code running in your browser.
The Windows menu key can be somewhat disabled, as described in this answer:
$(function(){
var lastKey=0;
$(window).on("keydown", document, function(event){
lastKey = event.keyCode;
});
$(window).on("contextmenu", document, function(event){
if (lastKey === 93){
lastKey=0;
event.preventDefault();
event.stopPropagation();
return false;
}
});
});

Line break on keydown

I have a textarea, and on each enter i want it to get blank if something has written. but my problem is; on the first enter it line breaks, and you continue to write from the second line. it only happens at the first enter. there is no problem with emptying the textarea, you just continue to write from the second line, which is the problem.
onkeydown= if(event.keyCode == 13){
sendMessage();
}
function sendMessage(user){
var message = $('#textarea').val();
$('#textarea').val('');
}

if(event.keyCode == 13) {
sendMessage();
if (event.preventDefault) event.preventDefault();
return false;
}
keydown happens before the character is entered in the textarea, so you just have to call preventDefault on the event so it doesn't enter a line break after you've called your function that clears the text-area. return false alone should be enough too if the code above is inline in the HTML, which isn't really recommended. See updated solution below:
For unobtrusiveness and back-compat, I'd recommend doing it all with jQuery:
$('#textarea_ID').keydown(function(e) {
if (e.which == 13) {
e.preventDefault();
var message = $(this).val();
$(this).val('');
//rest of your function using `message` here
}
});
Fiddle

In jQuery use the which property for the code. Then return false with e.preventDefault();
var field = $('.classname');
field.keydown(function(e){
if(e.which==13){
sendMessage();
e.preventDefault();
}
});

Simply add return false; to your keydown function. This prevents the default action of the key (a newline in this case) from being executed.
You may also want to include code to handle Internet Explorer's way of getting keycodes. Your new function would be:
onkeydown = function (e) {
// Gets keycode cross browser
e = window.event ? window.event : e;
var keycode = e.keyCode !== null ? e.keyCode : e.charCode;
// Checks if it was the enter key that was pressed (enter = keycode 13)
if (keycode === 13) {
// Calls function to do stuff
sendMessage();
// Cancels the default action of the (enter) key
return false;
}
}

keydown not working in firefox

<script>
function MoveNext(e, obj) {
if (!e) var e = window.event;
if (e.keyCode) code = e.keyCode;
else if (e.which) code = e.which;
if (code == 13) {
document.getElementById(obj).focus();
return false;
}
</script>
the above code is working in IE but not in mozilla why

change
if (e.keyCode) code = e.keyCode;
else if (e.which) code = e.which;
to
code = (e.keyCode)? e.keyCode: e.charCode;
and make sure your are passing your event to moveNext when you are calling it because firefox recognise event only if you sent it explicitly from the function.
also if your object that your are doing keydown is a div add to it a tabindex of 0 so it can retrieve focus .
<div id="mydiv" tabindex="0"></div>

Exactly what the best code is for the return key depends upon which keyboard event you are listening to (keydown, keyup, keypress). For keypress, you can do it like this:
function MoveNext(e, obj) {
e = e || window.event;
var code = e.which || e.keyCode;
if (code == 13) {
document.getElementById(obj).focus();
}
}
Note: I've remove your local variable e so it doesn't get confused with the argument e and I've defined code as a local variable which you had as an implicit global variable (never a good thing).
More on cross browser key handling described here: keycode and charcode.

How to listener the keyboard type text in Javascript?

I want to get the keyboard typed text, not the key code. For example, I press shift+f, I get the "F", instead of listen to two key codes. Another example, I click F3, I input nothing. How can I know that in js?

To do it document-wide, use the keypress event as follows. No other currently widely supported key event will do:
document.onkeypress = function(e) {
e = e || window.event;
var charCode = (typeof e.which == "number") ? e.which : e.keyCode;
if (charCode) {
alert("Character typed: " + String.fromCharCode(charCode));
}
};
For all key-related JavaScript matters, I recommend Jan Wolter's excellent article: http://unixpapa.com/js/key.html

I use jQuery to do something like this:
$('#searchbox input').on('keypress', function(e) {
var code = (e.keyCode ? e.keyCode : e.which);
if(code == 13) {
//Enter keycode
//Do something
}
});
EDIT: Since you're not binding to text box use:
$(window).on('keypress', function(e) {
var code = (e.keyCode ? e.keyCode : e.which);
if(code == 13) {
//Enter keycode
//Do something
}
});
http://docs.jquery.com/Main_Page

You can listen for the onkeypress event. However, instead of just examining either the event.keyCode (IE) or event.which (Mozilla) property which gives you the key code, you need to translate the key code using String.fromCharCode().
A good demo is at Javascript Char Codes (Key Codes). View the source and look for the displayKeyCode(evt) function.
Additional references: w3schools - onkeypress Event and w3schools - JavaScript fromCharCode() method.

This is too complicated to answer quickly. This is what I use as the definitive reference for keyboard handling. http://unixpapa.com/js/key.html

Problem with event handler

function getFieldName(e) {
e = e || window.event;
var key = e.keyCode || e.which,
target = e.target || e.srcElement;
alert(target.name);
return (key != 13);
}
I have the above function called on body tag onkeypress = getFieldName(event);
I get the name of desired field but not able to check in IE as well as FF
if(target.name == 'check') {
// works fine in FF but in IE I'm not able
// to come inside this if-block, please suggest
}
thanks

I see you've tagged this post as jQuery... If you actually use jQuery to manage the event handler then you can use e.which to find the key that was pressed and e.target to find the DOM target. It also worries about the cross-browser stuff for you.
To attach a function as an event handler, you can follow this simple example:
$(document).keypress(getFieldName);

jQuery already normalizes some event properties internally, so you can just use event.target and event.which, you don't need to check for others, like this:
$(document).keypress(getFieldName);
function getFieldName(e) {
alert(e.target.name);
if(e.which == 13) {
alert("Key pressed was enter");
} else {
alert("Key pressed was not enter");
}
}
​
You can view a quick demo here