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Javascript - getting the exact value of a textarea

I need to get the exact value of a textarea field. There are many topics, but none of them meet my needs.
Javascript transforms the html characters.
console.log(document.getElementById('t1').value);
// display: a'b => OK
console.log(document.getElementById('t2').value);
// display: a'b => KO I need to get a'b
<textarea id="t1">a'b</textarea>
<textarea id="t2">a'b</textarea>
I must imperatively recover the exact content of the textarea (and not re-encode the content).
Do you have a solution for this issue?

Not JavaScript is transforming anything when reading the textarea's value, but your browser is rendering the entities as their corresponding characters. So, once the page is rendered, there's no entity inside the textarea anymore, it's just the text as the end user would see it. Therefore, neither .value nor .innerHTML will be able to retrieve the entity.
If what you're trying to achieve is displaying entities inside a textarea, you'll have to double-encode them as a'b for example, by using the entity & for the ampersand.

Make my textbox understand html img tag

When inserting a new emoji inside my textbox i want to be displayed as the emoji image and not the emoji symbol how can i do that like instead of ( ':)'--> put the image represent it inside my textbox )

One way: Instead of a text box, use a <div contenteditable="true"></div>. As the user types, change occurrences of the smiley for the image. When the form is submitted, your javascript needs to translate the contents of that div back into plain text and put it into a field for submission.

If you want to use images, then it would require you to change your HTML significantly. You would need to make use of the Content Editable functionality on something like a <span>, rather than a regular input box. You'd then need JavaScript code to monitor keypress events and whenever it sees a :) (or whatever), it replaces the code with the appropriate <img>.
A quick-and-dirty solution that sticks with your text box, however, would be to use the same approach, but use the Unicode emoji characters (rather than images). This will only work on platforms with the appropriate font glyphs -- although the common smilies are more widely supported -- but it gives you the idea:
HTML:
<input class="emojify" type="text" />
JavaScript (using jQuery, to make everyone's life easier):
$(document).ready(function() {
// Map plaintext smilies to Unicode equivalents
var emoji = {
':)': '\u263a',
':(': '\u2639'
},
// Function to escape regular expressions
reEscape = function(s) {
return s.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
};
$('input.emojify').keyup(function() {
var text = $(this).val();
// See if any of our emoji exist in the text and replace with Unicode
$.each(emoji, function(plaintext, unicode) {
text = text.replace(new RegExp(reEscape(plaintext), 'g'), unicode);
});
// Replace text with new values
$(this).val(text);
});
});
Here's a working demo on jsFiddle. Note that the caret position will be reset every time the keyup event is triggered. I'm sure you can work around that somehow, but this code suffices to illustrate the process.

Preserving white space in an HTML select option

I have a set of html text boxes that take input and when the user clicks an 'add' button uses javascript to take the text input and format a string that is put in an HTML select box. The first of these boxes is supposed to contain a 2 character number but can also accept a blank. The formatted strings would look like this:
01-ABC-O
02-DEF-I
However I need a way to display the blank numbers that lines up with the other elements
-GHI-O
This type of entry will show up fine when the javascript adds the option, but when the page is reloaded and the select is repopulated with the values (I'm using Java, jsp, and struts 1.1 if that helps) it gets the same values(spaces preserved) but the whitespace is no longer shown in the select control (I've looked at the page source, and it looks identical to when the javascript adds the option). I have tried substituting the spaces for but this just prints the string "&nbsp" instead of the space. I've also tried using "pre" html blocks and the css white-space property and neither have worked.
Let me know if any further clarification is needed.

You need to replace the spaces with and it should work - note the closing semi-colon (which is missing from your example in the question)! When you do it through Javascript, most (all?) browsers will automatically render the spaces, but when the spaces are there when the page is loaded all (sometimes all but one) of them will be ignored.
You should also apply a font-family: CSS attribute to the select that specifies mono-spaced font(s) in order to ensure everything lines up properly.

When creating the select option with javascript, to preserve white-space, use "\xa0" - it is a NO-BREAK SPACE char.

You can use the pre css style on the area that you are outputting the value to.
<style type="text/css">
#element {
white-space: pre;
}
</style>
<div id="element">
stuff goes here
</div>
This will preserve all whitespace in the div element (other element types will also work) and then you don't need to worry about using the non breaking space.

Are you going to add it via scripting, you need to use Escape Codes for Space "% A0" which you then decode with unescape ()
logTypeList[i] = new Option(unescape(" kent Agent".replace(/ /g, "%A0")), "theValue");

logTypeList[i] = new Option(unescape(" kent Agent".replace(/ /g, "%A0")), "theValue");
Since unescape is deprecated, you may want to use decodeURI:
logTypeList[i] = new Option(decodeURI(" kent Agent".replace(/ /g, "%C2%A0")), "theValue");
More info at http://www.javascripter.net/faq/mathsymbols.htm

You can use the Unicode Character 'SPACE' (U+0020) instead of ("\u0020")

Displaying <textarea> value as HTML

I have a form with several textarea elements. User enters data and submits the form. On the next page it shows submitted text as static text - in p tags. Obviously New Line and multiple paces get ignored and everything just shows in one line.
I can do some preprocessing like replacing New line characters with "br/" and spaces with . but I was wondering if there is a standard solution to that either on server side (C#) or client side (javascript)

Since the data is preformatted (and this isn't just a matter of presentation), the pre element would be suitable (you will still need to replace <, & and friends with the appropriate entities).

Apply CSS white-space: pre; on the <p> element. This way any whitespace inside the element will be preserved.

Actually, I ended up replacing new line symbol with [br/] and it works very well.

Quote in HTML attribute destroys layout

My site has user generated content. I noticed that if the user has quotes in some text and later I displayed that text in an HTML attribute, the layout would get screwed up in IE.
Hello
However, if I had generated the same anchor with Javascript (Prototype library), the layout would not be screwed up in IE:
$$('body').first().appendChild(
new Element(
'a', {
title: 'user "description" of link',
href: 'link.html'
}
).update('Hello')
);
Why is this so? The JS and the plain HTML versions both have the same intended result, but only the JS doesn't screw up IE. What's happening behind the scenes?
BTW, I do strip_tags() and clean XSS attacks from all user input, but I don't strip all HTML entities because I use a lot of form text input boxes to display back user generated text. Form elements literally display HTML entities, which looks ugly.

You need to escape all output that is user-specified (using entities). The DOM-methods do that automatically.

I don't know how you are processing the user generated content, but you could use a replace function to clean up the input something like string.replace("\"", "")

The answer to your question: 'Why is it so' is because in your JavaScript example set the title attribute with single quotes. So the double quotes in the user generated string are already escaped.
In you A tag example, single quotes around the text you use in the title attribute may be a way to solve the rendering problem.
However, Your HTML attributes should be in double quotes, so you would be better off using entities, as suggested by #elusive in his answer.