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Javascript enabling input field after disable=true

html:
<label>Label1</label><br>
<input type="text" name="first" onclick="somefunc()"><br>
<label>Label2</label><br>
<input type="text" name="second"><br>
Javascript:
function somefunc() {
var second = document.getElementsByName('second')[0];
second.disable = true;
}
When I click the first input the second is disabled (that was what I want), but when I type something into the first input field, then delete it, the second is still disabled. Is there a way so I can enable it again?
I couldn't find an other event which can solve this.

You can listen to the keyup event on the first input box and check the value of first input box for enabling or disabling second input.
<label>Label1</label><br>
<input type="text" name="first" onkeyup="somefunc()"><br>
<label>Label2</label><br>
<input type="text" name="second"><br>
<script>
function somefunc() {
var first = document.getElementsByName('first')[0];
var second = document.getElementsByName('second')[0];
if(first.value){
second.disabled = true;
}else{
second.disabled = false;
}
}
</script>

Seems you have missed enabling textbox here. If you can see in previous reply, you just need to re-enable textbox into same state as it was before.

How to dynamically put a text from textbox to a label inside div using jquery

I have this Viewbag
<div id="amount"><h4>#ViewBag.Amount</h4></div>
How to I change the amount using jquery? I have this textbox
<input type="text" class="form-control" id="txtAmount" name="txtAmount" placeholder="Enter Amount" data-val="true" data-val-required="Amount to pay is required." data-val-number="Amount to pay must be a number.">
I have tried this code but it's not working
$("#btnSubmit").click(function () { $("amount").text(txtAmount); }

try this:
$("#amount").children('h4').eq(0).text($('#txtAmount').val());
please note though the above will not display as your submit button will submit your form. If you just want to update the value, you need to prevent the form submitting:
$("#btnSubmit").click(function (e) {
e.preventDefault();
$("#amount").children('h4').eq(0).text($('#txtAmount').val());
});
Also, it looks as if you are using the h4 for styling purposes - don't do this. Heading tags are for headings only. Use css to style the div tag

$("#btnSubmit").click(function () {
$("#amount>h4").text($('#txtAmount').val());
});

you are missing # in following statement
$("#btnSubmit").click(function () { $("amount").text(txtAmount); }
it should be
$("#btnSubmit").click(function () { $("#amount").text(txtAmount); }

Show placeholder instead of the default value in html form

A text field in html form have a default value,
but I would like to show the placeholder instead of the default value.
any ideas?

From what you said here it sounds like you actually want to listen for the focus and blur events and just clear the contents of the <input> with some kind of cache to restore it if nothing gets typed.
<input id="foo" type="text" value="" data-value="" />
Then in script
var foo = document.getElementById('foo');
foo.addEventListener('focus', function () {
this.setAttribute('data-value', this.value);
this.value = '';
});
foo.addEventListener('blur', function () {
if (this.value === '')
this.value = this.getAttribute('data-value');
});
DEMO

Provided you are only concerned with browsers that support HTML5, the following is an option:
<input type="text" name="myText" placeholder="My Placeholder">

<input type="text" name="foo" placeholder="Foo Name"/>
<input type="hidden" name="foo" value="foo"/>

On one hand, it is doable; on the other hand, I'm not sure why you should.
$('input[type="text"]').each(function (i, o) {
var inputBox = $(o),
swapInValue = function () {
inputBox.val(inputBox.data('val'));
},
swapOutValue = function () {
inputBox.data('val', inputBox.val()).val('');
};
inputBox.blur(swapOutValue).focus(swapInValue);
});

How to clear a text field?

I want to place a cross button next to a text field, which, on clicking it, clears the value entered by the user. In other words, it empties the field. Please help..
And I also want to focus the field, but after some 2 or 3 seconds..

Like this:
$('#myButton').click( function () {
$('#myField').val('');
});
Or without jQuery
document.getElementById('myButton').onclick = function () {
document.getElementById('myField').value = '';
});

Try this,
$('#button').click(function(){
$('#inputBox').val('');
});

Have you tried anything at all? But this should do (edit after misread, see below):
$('#your_button').click(function() { $('#your_textbox').val(''); });

In Javascript:
document.getElementById('textField1').value = "";

Well, learn to break your tasks into smaller one and everything will become much easier. Here, for example, you have 2 tasks:
1) Place a "X" button near input. This is achieved by CSS and HTML. You HTML might look like:
Then you should align your image with you input
2) Actual erasing. In jQuery:
$("#x_button").click( function() {
$("#input_id").val( "" );
});
But this is real basics of web development, so you should really consider to read some kind of book on it.

You can do it with html5 value.
<input type="text" placeholder="Your text here">

Assuming your text field looks like this one :
<input type="text" id="myText"></input>
and your button looks like this one :
<input type="button" id="myButton"></input>
You just have to do this in javascript :
<script type="text/javascript">
var myButton = document.getElementById('myButton');
myButton.addEventListener("click", function () {
document.getElementById('myText').value = '';
}, false);
</script>
If you're using jQuery it's even easier :
<script type="text/javascript">
$('#myButton').click(function() {
$('#myText').val('');
});
</script>

here is a sample:
Html:
<input type="text" id="txtText" value="test value" />
<input type="button" id="btnClear" value="Clear" />
javascript:
$(document).ready(function () {
$("#btnClear").click(ClearText);
});
function ClearText() {
$("#txtText").val("");
}

How can I get the value of an input field in javascript without submitting a form?

I'm fairly new to javascript and have a question about how to get a value of an input field without submitting a form. I have the following small piece of code, which I'm using in combination with a realtime-validation script to validate the fields.
<form name="FormName" method="post" />
<input type="text" id="nameValidation" value="HelloWorld" />
<script type="text/javascript">
var NameValue = document.forms["FormName"]["nameValidation"].value;
</script>
</form>
I want the var NameValue to be the value of what you type into the input field so I can use it in the message which appears after the validation. When I change the value of the input field without submitting the form, the var NameValue is stil set to "HelloWorld". After doing some research I found out I could solve it using jQuery and it's function serialize(). Is there a way to do this without jQuery?

Without jQuery :
var value = document.getElementById('nameValidation').value;
The syntax you had would be usable to get an input by its name, not its id.
If what you want is to use this value when it changes, you can do that :
var nameValidationInput = document.getElementById('nameValidation');
function useValue() {
var NameValue = nameValidationInput.value;
// use it
alert(NameValue); // just to show the new value
}
nameValidationInput.onchange = useValue;
nameValidationInput.onblur = useValue;

Your code works. It assign value of your input field to var NameValue. What you explained and what JQuery serialize does are two different things.
Everything you need is to assign your code to right event:
<form name="FormName" method="post" />
<input type="text" id="nameValidation" value="HelloWorld" onchange="myFunction()"/>
</form>
<script type="text/javascript">
function myFunction(){
var NameValue = document.forms["FormName"]["nameValidation"].value;
alert(NameValue);
}
</script>
​see the JSFiddle.

use the onchange or onblur event to call this code:
var NameValue = document.forms["FormName"]["nameValidation"].value;
This way it will get activated when the cursor leaves the textbox
<input type="text" id="nameValidation" value="HelloWorld" onblur="changeVal();" />
<script type="text/javascript">
function changeVal() {
var NameValue = document.forms["FormName"]["nameValidation"].value;
alert(NameValue);
}
</script>

In your example, the variable only gets the value assigned to it at that moment in time. It does not update when the textbox updates. You need to trigger a function [onchange or onblur or keypress] and reset the variable to the new value.
<form name="FormName" method="post" />
<input type="text" id="nameValidation" value="HelloWorld" />
<script type="text/javascript">
var myTextbox = document.getElementById("nameValidation");
var nameValue = myTextbox.value;
myTextbox.onchange = function() {
nameValue = myTextbox.value;
};
</script>
</form>

You can let your client-side code respond to a change in the value of the textbox, like so:
$(document).ready(function(){
$("#nameValidation").on('change', function() {
var value = $("#nameValidation").value;
//do your work here
}
})