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If keycode && input are not empty do something

I have barcode input in which I enter barcodes multiple times, every time I add barcode, barcode is added to the list even if I only press enter with empty value.
I want to start function only if user press enter key == 13 and value is not empty.
This is code:
if(key == 13) {}
I tried but without success:
var value = $("#barcode").val();
if(key == 13 && value.length > 0)
{alert("This works!")}...

You need to run your code under either the keyup or keypress event. Assuming you use jQuery to attach the event, you should also use the which property of the provided event object to get the keycode. Try this:
$('#barcode').keypress(function(e) {
if (e.which == 13 && this.value) {
alert("This works!")
}
})
Working example

Detect Tab Key event on textbox on focus

I have a autocomplete textbox in a form and I want to detect whether user has focussed on the textbox from navigating through tab key press.I mean tabindex has been set up on different form fields and user can navigate fields by pressing tabs.Now I want to perform some action when user directly mouse click/foxus on the textbox and some other action when user has focussed on the textbox through tab.
Below is the code I was trying.But no matter everytime code is 0.
$('#tbprofession').on('focus', function (e) {
var code = (e.keyCode ? e.keyCode : e.which);
if (code == 9) {
alert('Tabbed');
}
else
{
alert('Not tabbed');
}
});
This code does not work.
Note:Before marking duplicate it will be good if you understand the question correctly.Else I can make it more clear with more elaborated description.
Anyone can show me some light?

You can try something like that :
$(document).on("keyup", function(e) {
if ($('#tbprofession').is(":focus")) {
var code = (e.keyCode ? e.keyCode : e.which);
if (code == 9) {
alert('I was tabbed!');
} else {
alert('not tabbed');
}
}
});
fiddle : https://jsfiddle.net/xc847mrp/

You can use keyup event instead:
$('#tbprofession').on('keyup', function(e) {
var code = (e.keyCode ? e.keyCode : e.which);
if (code == 9) {
console.log('I was tabbed!', code);
}
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input autofocus>
<input id='tbprofession'>

You could have an array of key events triggered anytime a user presses a key while on your page. Although this makes you think of a keylogger.
Or just keep the last key.
Or a boolean saying if the last key pressed was a TAB or not.
And on focus you can look at that variable.

Disable submit a form in html when press Enter key

I have an HTML form with several text fields. So, I want to move cursor from a text field to next text field when I press the enter key, but the form should not be submitted. How can I do this? If there is a code example it may more helpful to me.

press the tab key on your keyboard instead of enter.

I'm using this function to do what you ask for:
$(document).on("keypress", ".TabOnEnter" , function(e)
{
if( e.keyCode == 13 )
{
var nextElement = $('[tabindex="' + (this.tabIndex+1) + '"]');
console.log( this , nextElement );
if(nextElement.length )
nextElement.focus()
else
$('[tabindex="1"]').focus();
}
});
Use the 'TabOnEnte' class on the fields you want this class to apply on.
Also to prevent user from submittin with enter key:
if (e.which == 13) {
e.preventDefault();
}

i got the answer. it should put in the input tag which we want.
onkeydown='if ((event.keyCode == 13 && document.getElementById("field_0").value!="") && event.which == 13){
document.getElementById("field_1").focus();
event.preventDefault();
}'

jQuery not detecting enter key pressed in textarea

My setup: jQuery 1.6.2
I have this HTML
<textarea class="comment_box"> Write a comment...</textarea>
And the following Javascript
<script>
$('.comment_box').keydown(function (e){
if(e.keyCode == 13){
alert('you pressed enter ^_^');
}
})
</script>
When I press the enter key in the textarea, nothing triggers
EDIT Oops, cut and paste error, I do have $ in my code and it still doesn't work, must be something else going on.
My bad, it is a user operator error, it does work. Sorry for the confusion.

$('.comment_box').keypress(function(event) {
// Check the keyCode and if the user pressed Enter (code = 13)
if (event.keyCode == 13) {
alert('you pressed enter ^_^');
}
});
Thats it

Check out this answer:
jQuery Event Keypress: Which key was pressed?
var code = (e.keyCode ? e.keyCode : e.which);
if(code == 13) { //Enter keycode
//Do something
}

For jQuery you need to use the $ to specify.
$('.comment_box').keyd
should do it.

Overwriting key events

How to overwrite or remove key events, that is on a website? I'm writing a script for GreaseMonkey and I want to make event on Enter button, but when I press the ENTER button, it triggers function on website.
EDIT 1: Here is the website, that I need to do this http://lockerz.com/auth/express_signup

One of these two should do it for you. I used the first one, although someone on SO told me the second one will work also. I went for the hammer.
Sorry, first one wasn't a cut and paste answer. I use using it to return up/down arrow control on a website. I changed it so that it identifies keycode 13 instead.
(function() {
function keykiller(event) {
if (event.keyCode == 13 )
{
event.cancelBubble = true;
event.stopPropagation();
return false;
}
}
window.addEventListener('keypress', keykiller, true);
window.addEventListener('keydown', keykiller, true);
})();

Searching quickly on SO:
jQuery Event Keypress: Which key was pressed?
Code from there:
var code = (e.keyCode ? e.keyCode : e.which);
if(code == 13) { //Enter keycode
//Do something
}

Without a library, use: http://jsfiddle.net/4FBJV/1/.
document.addEventListener('keypress', function(e) {
if(e.keyCode === 13) {
alert('Enter pressed');
return false;
}
});