Develop Reference

Responsive margin resizing

I want to have my elements resize their margins equally so that they fill the page. I tried turning the page width into a value using jquery but that didn't work.
var margen = $(window).width()
$(document).ready(function () {
$('#FixedMenu *').animate({
'margin-left': 'margen/6'
});
});
http://jsfiddle.net/clarinetking/2PGZS/40/

I make little update to your jsFiddle, you can see it here:
jsFiddle
What i change is this:
1.
You found width of screen:
var screenWidth = $(window).width();
2.
You found total width of child elements of your fixed menu
var widthOfChilds = 0;
$('#FixedMenu > *').each(function() {
widthOfChilds += $(this).outerWidth( true );
});
3.
You take off total width of child elements from screen size and you will get "free"width around child elements.
There are six of them, but you need space after last one from right, so you divide "free"width by number of childs + 1
var newmargin = (screenWidth - widthOfChilds)/7;
$('#FixedMenu *').animate({
'margin-left': newmargin
});
I hope it helped! :)

how to get html content width not window's width

I want to retrieve the html content width. Suppose when we resize the window to smaller size then scrollbar comes, so I want to get the width of the entire html content content that is visible and also the content the that is not visible due to the vertical scrollbar.

You can use window.outerWidth and window.innerWidth.

You may try this:-
var width = document.getElementById('foo').offsetWidth;
Try this code:
window.moveTo(0,0);
window.resizeTo(screen.width,screen.height);
var navButtonsEtcHeight = screen.height - window.innerHeight;
var navButtonsEtcWidth = screen.width - window.innerWidth;

Here's a Fiddle
<div></div>
$(function() {
var dWth = $(document).innerWidth(),
dHgt = $(document).innerHeight();
$('div').append('<h2>'+dWth+'px X '+dHgt+'px</h2>');
$(window).resize(function() {
var dWth = $(document).innerWidth(),
dHgt = $(document).innerHeight();
$('div').html('<h2>'+dWth+'px X '+dHgt+'px</h2>');
});
});
$(window).width(); // Returns width of browser viewport
$(document).width(); // Returns width of HTML document

You want the Element.clientWidth property. It gives the content width of the element.
Here's the documentation: https://developer.mozilla.org/en-US/docs/Web/API/CSS_Object_Model/Determining_the_dimensions_of_elements

function equalHeight , set a minimum Height to apply?

I have tried everything, but without javascript I cannot achieve the bad layout my designer gave to me!!
As you can see I have the div #backgr-box that has to be absolute positioned with z-index to be properly behind the #contenuto (which holds the page content!!)
Now to solve the extensibilty trouble of #backgr-box I have the below code that works if the content of #contenuto is longer than the sidebar #barra-laterale , but it is not ok in opposite case, see page: http://demo.liquidfactory.it/secondopolo/per-informarti
So how can I tell javascript to apply that calculation only over a minimum height of div sidebar #barra-laterale ??
Need help.. please!
function equalHeight(group) {
tallest = 0;
group.each(function() {
thisHeight = $(this).height();
if(thisHeight > tallest) {
tallest = thisHeight = $("#contenuto").height() - 380;
}
});
group.height(tallest);
}
$(document).ready(function() {
equalHeight($(".column"));
});

The problem is likely with this line:
tallest = thisHeight = $("#contenuto").height() - 380;
Currently it is setting both the variables tallest and thisHeight to the height of the content region minus 380 pixels. Change it to:
tallest = thisHeight;
And it will resize all the columns to the height of the tallest one.
Edit: It looks like your right-hand column actually consists of multiple columns with a class of .barra-laterale in this case you may want to take another tack altogether:
// calculate the total height of the content are and sidebar
var contentHeight = $("#contenuto").height();
var sidebarHeight = 0;
$(".barra-laterale").each(function() { sidebarHeight += $(this).height(); })
if (sidebarHeight > contentHeight) {
$("#contenuto").height(sidebarHeight);
} else {
// extend the last sidebar column to cover the difference between the
// height of the content and the sum of the sidebar heights
var lastSideBarHeight = $(".barra-laterale").last().height();
var heightDifference = contentHeight - sidebarHeight;
$(".barra-laterale").last().height(lastSideBarHeight + heightDifference)
}

Get elements width and height

How can i get height and width of element which doesn't a part of DOM yet?
For example:
var t = $('<div style="position:absolute;height:100px;width:100px;background-color:steelblue;" >lalala</div>');
var height = t.height(); // height is 0!

Works for me as well. You could try
var height = t.innerHeight();
though as demonstrated in this fiddle.
If that doesn't work for you (well possible depending on the browser), consider temporarily adding the element to the DOM:
var t = $('<div style="position:absolute;height:100px;width:100px;background- color:steelblue;" >lalala</div>').hide().appendTo('body');
var height = t.height();
t = t.detach().show();

Get image width/height units in JavaScript

I am creating an image object in JavaScript as
myImg = document.createElement('<img id=preview_image src="src/myImage.jpg" align="baseline" width="50%" height="80%"/>');
The image HTML will be obtained from database as in the given form.
Now, how can I get the height and width with the units (i.e. 50% for width in this case)?

var width = myImg.width, // width = '50%'
height = myImg.height; // height = '80%'
// or
width = myImg.getAttribute('width'),
height = myImg.getAttribute('height');

As documented every DOMElement has a ClientHeight and ClientWidth property, those will have the values you need.
https://developer.mozilla.org/en/DOM/element