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How do I make an html text input readonly but be able to update with a script?

I have these inputs that take the values of a from a in my table when I click on a row. I want to make it so that the user cannot change the input themselves but want to bring values into them when a user clicks a table row. I will be passing these inputs in as a form. I know that when the input is like this:
that it will not be updated. Is there any other way to do it with an input. Is there a different type of tag I can use that can be passed through a form?

Rather than a read-only <input>, I'd go with a combination of a display element and a hidden form element. Something like:
<div id="my-display">This is a value</div>
<input id="my-input" name="my-input" type="hidden" />
And in the code update both:
$('#my-display').text(yourValue);
$('#my-input').val(yourValue);
You can style the display to the user however you like and don't have to worry about whether or not it "de-activates" the form input.
If you really want it to be an inactive input, you can use the same approach:
<input class="my-input" type="text" disabled />
<input class="my-input" type="hidden" name="my-input" />
Which may even save you a line of code here, since both can now use .val():
$('.my-input').val(yourValue);

Try disabled keyword as here
<div id="my-display">This is a value</div>
<input id="my-input" name="my-input" type="text" disabled/>
You can change the value by javascript as below:
document.querySelector('#my-input').value = 'the value you want to enter by javascript';

to get <input> autofocussed so that a barcode scanner could input the productcode and my ajax function could handle it

I have the following code :
<input type="text" id="productCode" name="productCode" style="min-height: 42px;" onChange="ajaxrequest_provideProductListOnHit('protected/snippet/snippet_provideProductListOnHit.php', 'ajaxOnProductHit'); return false;" required="required" autofocus />
The problem is that :
The autofocus is not working, I'm using it in this input box only.
Actually the purpose of this input box is to get the field autofocussed so that a barcode scanner could input the productCode.
Now as you can see, my onChange event handler is not going to work here since the barcode scanner apart from the product code, inputs too.
So I need a solution here which autofocuses and once the barcode scanner inputs value in the field, calls for the mentioned ajax function.

html:
<input type="text" id="productCode" name="productCode" style="min-height: 42px;" required="required" autofocus />
js:
var pc = document.getElementById('productCode');
pc.onblur = function () {
ajaxrequest_provideProductListOnHit(
'protected/snippet/snippet_provideProductListOnHit.php',
'ajaxOnProductHit'
);
}
pc.focus();
i use onblur, because onchange would trigger after EVERY change you make (e.g. typing into the text-field will trigger after every key).
you could also provide some custom-logic, e.g. recognize a certain length

Yes you where right, the problem was that I was using autofocus on a different preceding form field which made this particular field of this particular form non-autofocus. So I learned that in a page with multiple forms loaded in to the DOM, only the first one with auto-focus will work. Fool of me to think otherwise.

jQuery - Changing value of input

I have this field in one form:
<input type="text" name="promocode" id="promoCode" value="" style="width:24%" maxlength="5">
and this field in another form:
<input type="hidden" name="custom" class="promo" value="" />
How can I do, so whenever the value of #promoCode is changed, it will also change the value of .promo
Currenlty, I have this:
var promo = $("#promoCode").val();
$("#promoCode").change(function(){
$('.promo').val(promo);
});
But that doesn't work.

$(function(){
$("#promoCode").change(function(){
$('.promo').val(this.value);
});
});
Make sure the DOM is ready when you attach your callback to the change event
this inside callback is the element the event attached to.
If you cache #promoCode value outside the change callback it will be out of sync right after the first change! use this.value inside the callback just like I did.

textbox should invoke button click event

I have a textbox and a button; the button click event navigates to other location in the website. I want to do the same thing on pressing the enter key but unable to do that. Please help me solve this. My code snippet follows:
function call()
{
document.location= "location.aspx";
}
<input type="text" id="txt1" onkeydown ="if(event.keyCode==13)document.getElementById('bt1').click()"/>
<input type="button" id="bt1" value ="Hit me" onclick ="call()" />

This is the same as the click, both would call this function...
onkeydown ="if(event.keyCode==13) call()"

If you can edit your HTML code, you wont probably need to do any JS to get this to working.
The INPUT fields in your HTML should be wrapped inside a FORM tag (atleast thats how it semantically makes more sense in most of the cases).
If you can do that, you can then change the INPUT element from TYPE button to Type SUBMIT and can then listen for the onsubmit event on your FORM element.
The event is fired both on pressing of enter key and click of the button and it works pretty smoothly across the browsers. The only problem is IE which doesnt fire the onsubmit event on a form with just 1 text input field. For that, you will have to insert another field into the form. You can hide it for your case. More ref at : http://style-vs-substance.com/development/form-submit-by-enter-key-and-internet-explorer/
EDIT: Code Sample
<form id="myForm">
<!--[if IE]>
<input type="text" style="display: none;" disabled="disabled" size="1" /><![endif]-->
<input type="text"/>
<input type="submit" value="Search"/>
</form>
Then in your JS:
var formHandler = document.getElementById('myForm');
formHandler.onsubmit = function(){
//this callback will be invoked both by the search button and enter key now
//your logic here
}

How to skip fields using javascript?

I have a form like this:
<form name="mine">
<input type=text name=one>
<input type=text name=two>
<input type=text name=three>
</form>
When user types a value in 'one', I sometimes want to skip the field 'two', depending on what he typed. For example, if user types '123' and uses Tab to move to next field, I want to skip it and go to field three.
I tried to use OnBlur and OnEnter, without success.
Try 1:
<form name="mine">
<input type=text name=one onBlur="if (document.mine.one.value='123') document.three.focus();>
<input type=text name=two>
<input type=text name=three>
</form>
Try 2:
<form name="mine">
<input type=text name=one>
<input type=text name=two onEnter="if (document.mine.one.value='123') document.three.focus();>
<input type=text name=three>
</form>
but none of these works. Looks like the browser doesn't allow you to mess with focus while the focus is changing.
BTW, all this tried with Firefox on Linux.

Try to attach tabindex attribute to your elements and then programmaticaly (in javaScript change it):
<INPUT tabindex="3" type="submit" name="mySubmit">

You could use the onfocus event on field two, which will be called when it receives focus. At that point, field 1's value should be updated and you can perform your check then.

If you used the method you describe, and they worked, the focus would also change when the user clicks on the field, instead of tabbing to it. I can guarantee you that this would result in a frustrated user. (Why exactly it doesn't work is beyond me.)
Instead, as said before, change the tabindex of the appropriate fields as soon as the content of field one changes.

<form name="mine">
<input type="text" name="one" onkeypress="if (mine.one.value == '123') mine.three.focus();" />
<input type="text" name="two">
<input type="text" name="three">
</form>

Try onkeypress instead of onblur. Also, on the onfocus of field two is where you should be sending to three. I'm assuming you don't want them typing in two if one is 123 so you can just check that on two's onfocus and send on to three.