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Fix double call and get before value

I am learning JQuery by example. Please check this fiddle: http://jsfiddle.net/4tjof34d/2/
I have two problems:
1 : showText() gets called twice when a person hits enter and thus console.log(this.id+ " " +this.value); gets called twice, What do I add so that it only gets called once?
2: I get the id and value of the textbox, but I also want to know what was the old id and value so that I can do a comparison test. How do I do that?
eg:
var oldValue = ? // How do I do this?
var newValue = this.value;
Then I can do something like:
if(newValue != oldValue)
{
// Do .ajax() - update DB
}

for your first issue showText is called twice ie,on blur and on enter
change your blur function as follows
$('.input').blur(showText).keyup(function (e) {
if(e.which === 13) {
this.blur();
}
});
for second issue i will go with a global variable as flag
http://jsfiddle.net/x1ez7Lek/6/

jQuery trigger keyup on input gets old value

I try to manually trigger key-up event in qunit test but it fails since manually trigger key-up event will not change the input value.
http://jsfiddle.net/Re9bj/4/
$('input').on('keyup', function (event) {
$('div').html($('input').val());
});
var e = $.Event('keyup', {
keycode: 68
});
$('input').trigger(e); //this trigger will not change the input value
This trigger will work but the problem is that input value never change.

You can't add a character with a simple trigger. Trigger will only fire events, but not the default behavior. You need to simulate it.
To do that, you can use this code :
if(event.isTrigger && event.keycode) this.value += String.fromCharCode(event.keycode);
It will check if the event is triggered and then print the value.
Final code :
$('input').on('keyup', function (event) {
if(event.isTrigger && event.keycode) this.value += String.fromCharCode(event.keycode);
$('div').html($('input').val());
});
var e = $.Event('keyup', {
keycode: 68
});
$('input').trigger(e);
Fiddle : http://jsfiddle.net/Re9bj/9/

jQuery-Enter key event function alerts repeatedly

I have to prevent the form submit if the newVal and oldVal are equal. Else I need to execute the Javascript function. - While pressing Enter key from the key board for the dynamically generated textboxes.
For this case, While pressing enter key the alert is coming repeatedly.
ie, first time one alert. Two alerts for second time.And the expected result is not getting.
What is expected: If I enter a value equals to the curValue then form doesn't have to submit.Else need to call the function myFun(); What is wrong with me?
function pressEnter(id,newValue,i)
{
var newId = '#'+id;
$(newId).keydown(function(event) {
var curValue= '<%=currentVal%>';
var keycode = (event.keyCode ? event.keyCode : event.which);
if(keycode == '13'){
alert(newValue+"-"+curValue);
if(newValue== curValue)
{
event.preventDefault();
}
else
{
myFun(i);
}
}
});
}

You have to unbind previous keydown handler:
$(newId).off('keydown').keydown(function(event) {...});

You can do this comparison on form submit event rather than pressing enter key. Because user can use mouse and click the submit button.
Restrict user on form submit as follows,
$("#your_form_id").submit(function() {
var newValue = $(".your_textbox").val();
var curValue= '<%=currentVal%>';
if(newValue== curValue)
{
event.preventDefault();
//Or use return false;
} else{
myFun();
}
});
Here, we can avoid unwanted bind and unbind operations.
And we can achieve this on enter press, just write without function as follows,
$("#your_text_box_id").keydown(function(event) {
var newValue = $(".your_textbox").val();
var curValue= '<%=currentVal%>';
var keycode = (event.keyCode ? event.keyCode : event.which);
if(keycode == '13'){
alert(newValue+"-"+curValue);
if(newValue== curValue)
{
event.preventDefault();
}else{
myFun();
}
}
});
Note: If you scope this jQuery code within a function,then javascript add handler for same event on every function call. Result is your code(Code in "keydown" callback) run multiple time. To avoid you have to unbind the event.

Re-enabling Submit after prevent default

I am trying to unbind or reenable the prevent default so my form will submit on good data.
I have tried multiple examples. Here is my code and some of the examples i tried.
This code works great for what i want to. Just the last thing and resetting the div which i can implement after i get this.
function lengthRestriction(elem, min, max) {
var uInput = elem.value;
if (uInput.length >= min && uInput.length <= max) {
return true;
} else {
var cnt = document.getElementById('field');
cnt.innerHTML = "Please enter between " + min + " and " + max + " characters";
elem.focus();
$('#ShoutTweet').submit(function(e) {
e.preventDefault();
//bind('#ShoutTweet').submit();
//$('#ShoutTweet').trigger('submit');
});
}
}​
i have a jsbin set up too http://jsbin.com/ebedab/93

Don't try to set up and cancel a submit handler from within your validation function, do it the other way around: call the validation from within a single submit handler, and only call .preventDefault() if the validation fails:
$(document).ready(function() {
$('#ShoutTweet').submit(function(e) {
if (/* do validations here, and if any of them fail... */) {
e.preventDefault();
}
});
});
If all of your validations pass just don't call e.preventDefault() and the submit event will then happen by default.
Alternatively you can return false from your submit handler to prevent the default:
$('#ShoutTweet').submit(function(e) {
if (!someValidation())
return false;
if (!secondValidation())
return false;
if (someTestVariable != "somevalue")
return false;
// etc.
});

I'm not completely sure what you are asking, but if your goal is to destroy your custom submit handler, then use this:
$("#ShoutTweet").unbind("submit");
This assumes that you have a normal (not Ajax) form.

Just call submit on the form
$('#ShoutTweet').submit();

This works surely and enable form submission after event.preventDefault();
$('#your-login-form-id').on('submit', onSubmitLoader);
function onSubmitLoader(e) {
e.preventDefault();
var self = $(this);
setTimeout(function () {
self.unbind('submit').submit(); // like if wants to enable form after 1s
}, 1000)
}

Need help on change event on both input boxes

i need help on this one....i want to trigger the alert() e.g some code to execute after the change event on both input boxes....here is my code..
Millimeter: <input type="text" id="millimeter" class="filter"/>
Inch: <input type="text" id="inch" class="filter"/>
<script type="text/javascript">
$(document).ready(function(){
$(".filter").change(function(){
var value = this.value;
var id = this.id;
var convert = "";
switch(id)
{
case "millimeter":
convert = (value / 25.4).toFixed(2); //converts the value of input(mm) to inch;
$("#inch").val(convert).change();
break;
case "inch":
convert = (value * 25.4).toFixed(2); //converts the value of input(inch) to mm;
$("#millimeter").val(convert).change();
break;
default:
alert('no input has been changed');
}
alert(id+" triggered the change() event");
//some code here....
});
});
</script>
what i want is to trigger the alert() 2 twice...the result would be look like this..."Millimeter triggered the change() event"...and then when the other input box changes its value...."Inch triggered the change() event"....vice versa...i'm new to javascript and jquery...any help would be much appreciated..

The problem with your code is that in the change event of the first textbox you are triggering the change event of the second and thus entering in an endless loop. You should only use the following:
$("#inch").val(convert);
and:
$("#millimeter").val(convert);
in order to set the value of the other field but do not trigger change again.

Running your script on jsFiddle got me a "Maximum call stack size exceeded" error. This is because you're calling your .change() function inside of itself. I removed it, and it works fine.
Fiddle: http://jsfiddle.net/EwdLs/
$(".filter").change(function() {
var value = this.value;
var id = this.id;
var convert = "";
switch (id) {
case "millimeter":
convert = (value / 25.4).toFixed(2); //converts the value of input(mm) to inch;
$("#inch").val(convert);
break;
case "inch":
convert = (value * 25.4).toFixed(2); //converts the value of input(inch) to mm;
$("#millimeter").val(convert);
break;
default:
alert('no input has been changed');
}
alert(id + " triggered the change() event");
//some code here....
});

If you want each input's change to also trigger the other input's change, but don't want to get in an endless loop, try some variation on the following:
$(document).ready(function(){
function applyChange(el, changeOther) {
var value = el.value;
var id = el.id;
var convert,
other = "";
if (changeOther) {
switch(id) {
case "millimeter":
convert = (value / 25.4).toFixed(2);
other = "#inch";
break;
case "inch":
convert = (value * 25.4).toFixed(2);
other = "#millimeter";
break;
default:
alert('no input has been changed');
break;
}
if (other != "") {
$(other).val(convert);
applyChange($(other)[0], false);
}
}
alert(id+" triggered the change() event");
//some code here....
}
$(".filter").change(function(){
applyChange(this, true);
});
});
In case it's not obvious, I basically took your existing change handler and put it in a new function, applyChange, which has a parameter to tell it whether or not to recurse. The code as is is clunky, but it should give you the general idea of one way to do what you seem to be asking.
P.S. Be sure to add in some validation that what the user entered is really a number.