Develop Reference

how to reformat jQuery / JS function properly?

can't figure out how to write this as a function without the jQuery
This works & returns what I need:
var state = $('#order_ship_address_attributes_state_id option:selected').text()
Which is the text from an options list aka "Florda" instead of "3534"
<option value="3534">Florida</option>
However, I would like it written in this convention instead:
var city = ((document.getElementById('order_ship_address_attributes_city')||{}).value)||"";
... to match the rest of my variable declarations.
Trying this but error read "Uncaught TypeError: Cannot read property 'text' of null"
var state = ((document.getElementById('order_ship_address_attributes_state_id option:selected')).text())
Can't figure out the correct way to write this — any help would be much appreciated : )

As #benvc pointed out. You want to use .textContent instead of calling the .text() jquery method.

Using function as an attribute for div in jQuery

Since my selector options and logo images have the same names i want to use this to make a function that changes the image when you select. I've tried this:
$(function(){
$(selector).click(
$(function(){
$(div).attr("src", "($(selector).val()).png")
}))})
Buuut, no sauce :(
With help from parth718 got to this:
$(function)(){
$(selector).click($(div).attr("src", "images/logos/"+($(selector).val()+".png")))};
But now i'm getting error: TypeError: g.handler.apply is not a function.
I'm running jQuery 1.12.2 from Google's CDN on this.
Toughts? .-.

In PHP, "$file.png" gives you the result you want, not in javascript ...
You have to concatenate strings with your var with the plus operator.
As said, you have to do a :
$(logodiv).attr("src", $(selector).val()+".png")

instead of
$(logodiv).attr("src", "($(selector).val()).png");
try this
$(logodiv).attr("src",($(selector).val()+".png");
You are using variable inside "" therefore the attr will be changed as
src="$(selector).val().png"
exact string will be there and not the selector variable.

When I'm trying to append data-id; I got an error

Check this out:
here's a simple code that works fine
html
<select></select>
<button id="btn1">click me</button>
js
$('#btn1').on('click',function(){
var select = $('select');
select.append($('<option>').val('v2').text('text2'));
});
When I'm trying to append data-id I got an error. Any help?
select.append($('<option>').val('v2').text('text2').data-id('id1'));
http://jsfiddle.net/omarmakled/QQ44U/

You can do this 2 ways
select.append($('<option>').val('v2').text('text2').attr('data-id','id1'));
or
select.append($('<option>').val('v2').text('text2').data('id', 'id1'));
http://api.jquery.com/data/
http://api.jquery.com/attr/

First, data-id string is illegal identifier in JS (as it contains hyphen), therefore even if it were available as a jQuery object method, you should have called it like that...
someObj['data-id'](someId);
Apparently, that's too messy for such a simple operation. In fact, there's no such method defined in jQuery.prototype - which instead expects you to employ either attr() (to set any attribute explicitly), or data() (dataset API specific one).
As a sidenote, you don't have to make that many calls: this...
select.append($('<option>', {
value: 'v2',
text: 'text2',
'data-id': 'id1'
}));
... is both more readable AND efficient. Note the quotation marks around 'data-id': object properties can be non-quoted only if they are proper JS identifiers.
JSFiddle.

The correct method to use is data():
select.append($('<option>').val('v2').text('text2').data('id','id1'));
Or if you want an actual attribute you can use attr():
select.append($('<option>').val('v2').text('text2').attr('data-id','id1'));

Add non-standard attribute to a select tag with Javascript

I want to create a select element through JavaScript and I want to set an attribute to it called data-placeholder.
How can we assign non-standard attributes with JavaScript without the browser complaining with:
Uncaught referenceError: Invalid left-hand side in assignment
Code that cause the error:
select1.data-placeholder="Choose ...";

Since it says with javascript not jquery...
yourElement.setAttribute('data-placeholder','value');

Here's a pretty simple non-jQuery way to achieve this;
var el = document.createElement('select');
el.setAttribute('data-placeholder', 'placeholder value');
document.body.appendChild(el);​
I've created a very simple JSFiddle to demonstrate it.
Hope that helps!

JQuery makes this easy:
$("<select></select>").attr("data-placeholder", "value").appendTo($element);

How do I set the value of an input-element via jQuery, when I only know it's "name"-attribute

I need to reset some text-boxes which only have an unique name (not an unique id).
I tried it with jQuery, but my code seems to do nothing:
$('input[name=customergroupname]').value="";

Try this:
$('input[name="customergroupname"]').val("");

Getting and setting value of form elements wrapped in a jQuery object is being done with use jQuery val function:
$('input[name="customergroupname"]').val("");
.value can only be used for DOM elements, like this:
$('input[name="customergroupname"]').eq(0).value ="";
$(...) // This is a jQuery object.
$(...)[n] // This is a DOM object in the nth place in the set.
$(...).eq(n) // This is a DOM object in the nth place in the set.

Working demo http://jsfiddle.net/vN74v/2/
Code
$('#hullk').click(function(){ // in example when you click the button
$('input[name="customergroupname"]').val("");
});
​

According to DOM level 2 specifications, you can access:
document.forms["foo"].elements["customergroupname"].value = '';
If formName and fieldName are constants rather than variables you can use literal syntax:
document.forms.foo.elements.customergroupname.value = '';

try:
$('input[name="customergroupname"]').value="";
I've wrapped customergroupname in quotes.
Very true, I mixed the quotes up. Edited now.