Develop Reference

Where can I find documentation for this weird behavior of `Element.querySelector`

While debugging a validation routine, I ran across this odd behavior with Element.querySelector where I pass a selector to it that should target select elements and it returned, not just one, but every option element that is child of the targeted select.
Example:
(() => {
const handlerWeird = (e) => {
const select = Array.from(document.querySelector('#i-am-a-select'));
console.log(select);
};
const handlerNormal = (e) => {
const select = Array.from(document.querySelectorAll('#i-am-a-select'));
console.log(select);
};
document.getElementById('weirdness').addEventListener('click', handlerWeird, false);
document.getElementById('normalness').addEventListener('click', handlerNormal, false);
})();
<select id="i-am-a-select">
<option value="weird">weird</option>
<option value="doubly-so">doubly so</option>
</select>
<button id="weirdness">Weirdness</button>
<button id="normalness">Expected</button>
Switching to Element.querySelectorAll (and filtering the resultant nodelist) returned the select element I needed, so while my specific problem has been fixed, the question remains why does this behavior happen and assuming it is documented anywhere, where is is documented?
Tested in Chrome (v 65.0.3325.181) and FireFox Quantum (v 58.0.2).

That's because document.querySelector('#i-am-a-select') is returning a single HTMLSelectElement.
Array.from() will create an array from an array-like object, or from an iterable object.
An HTMLSelectElement is an array-like object, where each item is an option, inside the element.
See this example:
const selectElement = document.querySelector('#i-am-a-select');
console.log('First option: ', selectElement[0]);
const select = Array.from(selectElement);
console.log(select);
<select id="i-am-a-select">
<option value="weird">weird</option>
<option value="doubly-so">doubly so</option>
</select>
So, since this element is an "array-like object", Array.from() will return an array with its options.
Careful though:
Even though you can run trough the HTMLSelectElement's items, it doesn't means this element is an array. To create an array from it, you'll use Array.from().
See this other example:
const selectElement = document.querySelector('#i-am-a-select');
selectElement.forEach(function(){ //will throw an Error
console.log(this);
});
<select id="i-am-a-select">
<option value="weird">weird</option>
<option value="doubly-so">doubly so</option>
</select>

You selected a select element:
https://dev.w3.org/html5/spec-preview/the-select-element.html
select[index]
Returns the item with index index from the list of options. The items are sorted in tree order.
It's nothing to do with querySelector, nor really Array.from - it's all due to the behavior of select elements themselves. someSelectElement[i] will return the ith option. Convert the element to a plain array, and... the same thing happens, someSelectElement[i] will return the ith option
const select = document.querySelector('select');
console.log(select[0]);
console.log(select[1]);
<select>
<option>1</option>
<option>2</option>
</select>

Load array of Enum values from Json file

I have a local JSON file containing all of my Enum key-value pairs and would like to load them into an array that I can use easily.
enum.json
{
"AbsenceCode": {
"E": "Excused",
"U": "Unexcused"
},
"ActiveInactive": {
"A": "Active",
"I": "Inactive"
},
"AuthenticationLog": {
"1": "Staff",
"2": "ParentAccess",
"3": "StudentAccess"
},
"YesNo": {
"0": "Yes",
"1": "No"
}
}
In my Javascript code, I want to load all of the key-value pairs into an array or object that allows me to easily access them, with the end goals of (a) doing value lookup and (b) creating select boxes.
I started something like this but I'm not wrapping my mind around it correctly and also somewhat unsure of whether this should be done with an array or an object, and whether JavaScript allows the type of array necessary to do this.
// load enumData
var enumKeys = $.getJSON("enum.json", function(json) {
var array = [];
for (var key in json) {
var item = json[key];
for (var keyvalue in item) {
var value = item[keyvalue];
}
array.push(parsed[key])
}
});
// test enumData
console.log(enumKeys["YesNo"]);
// lookup value of key
console.log(enumKeys["AbsenceCode"]["U"]);
In my Aurelia template, I would want something like this:
<template>
<select ref="absencecode">
<option repeat.for="keyvalue of enumKeys.AbsenceCode" value="${keyvalue.key}">${keyvalue.value}</option>
</select>
</template>
My code is "inspired" by the answers to a lot of other similar cases but I didn't find any that matched this exact scenario. Any help would be appreciated! What code should I use to load enumKeys? How do I use the loaded array/object?

You could use a Value Converter to process object. In fact, there is a nice example for that in the [Documentation, last section].
Applying above example to your case, it's even possible to process objects without any prior transformation.
Gist demo: https://gist.run/?id=4514caa6ee7d40df2f7cfe2605451a0e
I wouldn't say it’s the most optimal solution, though. You might want to transform the data somehow before passing it to repeat.for.
Just showing a possibility here.
Template:
<!-- First level properties -->
<div repeat.for="mainKey of data | keys">
<label>${mainKey}</label>
<!-- Sublevel - Value Object properties -->
<select>
<option value="">---</option>
<option repeat.for="code of data[mainKey] | keys"
value="${code}">${data[mainKey][code]}</option>
</select>
</div>
keys value converter:
export class KeysValueConverter {
toView(obj) {
return Reflect.ownKeys(obj);
}
}
Update:
But how do I target one specific item without having to iterate over all of them?
I've extended the original gist demo, you can check it out.
This would work, but it wouldn't be reusable
<label>Absence Code</label>
<select>
<option value="">---</option>
<option repeat.for="code of data.AbsenceCode | keys"
value="${code}">${data.AbsenceCode[code]}</option>
</select>
A better way would be to create a custom element
(Note: <require> is there for demo purposes. Normally, you'd add it to globalResources.)
Organizing above template into a custom element with source and name bindable properties:
source: your data object
name: first-level property of data object (e.g. AbsenceCode)
enum-list.html
<template>
<require from="./keys-value-converter"></require>
<label>${name}</label>
<select name="${name}" class="form-control">
<option value="">---</option>
<option repeat.for="code of source[name] | keys" value="${code}">${source[name][code]}</option>
</select>
</template>
You can also use name property in conjunction with aurelia-i18n to display a meaningful label. E.g. ${name | t}.
enum-list.js
import {bindable} from 'aurelia-framework';
export class EnumList {
#bindable source;
#bindable name;
}
Usage
Individual dropdowns:
<enum-list source.bind="data" name="AbsenceCode"></enum-list>
<enum-list source.bind="data" name="AuthenticationLog"></enum-list>
Since <enum-list> has all the data, its name property can also be changed at runtime! :)
<label>Type</label>
<select class="form-control" value.bind="selectedType">
<option repeat.for="mainKey of data | keys" value="${mainKey}">${mainKey}</option>
</select>
<br>
<enum-list source.bind="data" name.bind="selectedType"></enum-list>

You could use aurelia-fetch-client as described here http://aurelia.io/hub.html#/doc/article/aurelia/fetch-client/latest/http-services/2
For example:
import {HttpClient} from 'aurelia-fetch-client';
let client = new HttpClient();
client.fetch('package.json')
.then(response => response.json())
.then(data => {
console.log(data.description);
});

assign a object to select value - ng-options

I have a object like this
var myObject = {'123':'something','345':'something else'}
I need to render it as:
<option value={'123':'something'}>something</option>
Here is what i have tried:
ng-options="someObj as label for (id,label) in myObject
Doesn't work!
The model gets the 'label' and not the whole object. Is it even possible to assign a object to value attribute of a SELECT element?
EDIT
Filter for object of the form: {'123':'something','345':'something else'}
.filter('putKeysandValues',function(){
return function(options){
var arr = [];
angular.forEach(options,function(value,key){
arr.push({'key':key,'label':value})
});
return arr;
}
});

You will need to provide an object with key & value attributes to ngOptions. For this you will need to modify the structure of your object to actually have this attributes.
One way is using a filter that returns a valid array for ngOptions:
ng-options="option.label for option in data.availableOptions | putKeyAndValue"
You can check out this plunker with a working filter.
If input is:
[{'123':'something'}, {'345':'something else'}]
Then output is:
[{"123":"something","id":123,"label":"something","$$hashKey":"object:3"},{"345":"something else","id":345,"label":"something else","$$hashKey":"object:4"}]
If you want to remove the obsolete id attribute, then use this filter.
With input the same input, it will return this:
[{"id":123,"label":"something","$$hashKey":"object:3"},{"id":345,"label":"something else","$$hashKey":"object:4"}]
If you still need to return a new array, then do not do it on the filter. In that case you can process the data before passing it to the view, all in the controller like this.
With input:
{'123':'something', '345':'something else'}
Output this:
[{"id":123,"label":"something"},{"id":345,"label":"something else"}]

Using select as something for a (key,value) in set of Values
ng-options="key as value for (key,value) in myObject"
This will put key into the option value and value into label. With that you need to also use ng-model and ngChange. Since you can't pass objects into values, idea is to do that in your controller.
<select ng-model="val" ng-change="changeVal(val)" ng-options="key as value for (key,value) in ops">
In your controller you already have myObject you are gonna add selected item and changeVal function
<script>
var selectedObject;
$scope.changeVal = function(val){
selectedObject = {};
selectedObject[val] = myObject[val];
}
</script>
It's a workaround without putting object into value attr since it is a string.

How do I set the value property in AngularJS' ng-options?

Here is what seems to be bothering a lot of people (including me).
When using the ng-options directive in AngularJS to fill in the options for a <select> tag, I cannot figure out how to set the value for an option. The documentation for this is really unclear - at least for a simpleton like me.
I can set the text for an option easily like so:
ng-options="select p.text for p in resultOptions"
When resultOptions is for example:
[
{
"value": 1,
"text": "1st"
},
{
"value": 2,
"text": "2nd"
}
]
It should be (and probably is) the most simple thing to set the option values, but so far I just don't get it.

See ngOptions
ngOptions(optional) – {comprehension_expression=} – in one of the
following forms:
For array data sources:
label for value in array
select as label for value in array
label group by group for value in array
select as label group by group for value in array track by trackexpr
For object data sources:
label for (key , value) in object
select as label for (key , value) in object
label group by group for (key, value) in object
select as label group by group for (key, value) in object
In your case, it should be
array = [{ "value": 1, "text": "1st" }, { "value": 2, "text": "2nd" }];
<select ng-options="obj.value as obj.text for obj in array"></select>
Update
With the updates on AngularJS, it is now possible to set the actual value for the value attribute of select element with track by expression.
<select ng-options="obj.text for obj in array track by obj.value">
</select>
How to remember this ugly stuff
To all the people who are having hard time to remember this syntax form: I agree this isn't the most easiest or beautiful syntax. This syntax is kind of an extended version of Python's list comprehensions and knowing that helps me to remember the syntax very easily. It's something like this:
Python code:
my_list = [x**2 for x in [1, 2, 3, 4, 5]]
> [1, 4, 9, 16, 25]
# Let people to be a list of person instances
my_list2 = [person.name for person in people]
> my_list2 = ['Alice', 'Bob']
This is actually the same syntax as the first one listed above. However, in <select> we usually need to differentiate between the actual value in code and the text shown (the label) in a <select> element.
Like, we need person.id in the code, but we don't want to show the id to the user; we want to show its name. Likewise, we're not interested in the person.name in the code. There comes the as keyword to label stuff. So it becomes like this:
person.id as person.name for person in people
Or, instead of person.id we could need the person instance/reference itself. See below:
person as person.name for person in people
For JavaScript objects, the same method applies as well. Just remember that the items in the object is deconstructed with (key, value) pairs.

How the value attributes gets its value:
When using an array as datasource, it will be the index of the array element in each iteration;
When using an object as datasource, it will be the property name in each iteration.
So in your case it should be:
obj = { '1': '1st', '2': '2nd' };
<select ng-options="k as v for (k,v) in obj"></select>

I had this issue too. I wasn't able to set my value in ng-options. Every option that was generated was set with 0, 1, ..., n.
To make it right, I did something like this in my ng-options:
HTML:
<select ng-options="room.name for room in Rooms track by room.price">
<option value="">--Rooms--</option>
</select>
I use "track by" to set all my values with room.price.
(This example sucks: because if there were more than one price equal, the code would fail. So BE SURE to have different values.)
JSON:
$scope.Rooms = [
{ name: 'SALA01', price: 100 },
{ name: 'SALA02', price: 200 },
{ name: 'SALA03', price: 300 }
];
I learned it from blog post How to set the initial selected value of a select element using Angular.JS ng-options & track by.
Watch the video. It's a nice class :)

If you want to change the value of your option elements because the form will eventually be submitted to the server, instead of doing this,
<select name="text" ng-model="text" ng-options="select p.text for p in resultOptions"></select>
You can do this:
<select ng-model="text" ng-options="select p.text for p in resultOptions"></select>
<input type="hidden" name="text" value="{{ text }}" />
The expected value will then be sent through the form under the correct name.

To send a custom value called my_hero to the server using a normal form submit:
JSON:
"heroes": [
{"id":"iron", "label":"Iron Man Rocks!"},
{"id":"super", "label":"Superman Rocks!"}
]
HTML:
<select ng-model="hero" ng-options="obj.id as obj.label for obj in heroes"></select>
<input type="hidden" name="my_hero" value="{{hero}}" />
The server will receive either iron or super as the value of my_hero.
This is similar to the answer by #neemzy, but specifying separate data for the value attribute.

It appears that ng-options is complicated (possibly frustrating) to use, but in reality we have an architecture problem.
AngularJS serves as an MVC framework for a dynamic HTML+JavaScript application. While its (V)iew component does offer HTML "templating," its primary purpose is to connect user actions, via a controller, to changes in the model. Therefore the appropriate level of abstraction, from which to work in AngularJS, is that a select element sets a value in the model to a value from a query.
How a query row is presented to the user is the (V)iew’s concern and ng-options provides the for keyword to dictate what the contents of the option element should be i.e. p.text for p in resultOptions.
How a selected row is presented to the server is the (M)odel’s concern. Therefore ng-options provides the as keyword to specify what value is provided to the model as in k as v for (k,v) in objects.
The correct solution this is problem is then architectural in nature and involves refactoring your HTML so that the (M)odel performs server communication when required (instead of the user submitting a form).
If an MVC HTML page is unnecessary over-engineering for the problem at hand: then use only the HTML generation portion of AngularJS’s (V)iew component. In this case, follow the same pattern that is used for generating elements such as <li />'s under <ul />'s and place a ng-repeat on an option element:
<select name=“value”>
<option ng-repeat=“value in Model.Values” value=“{{value.value}}”>
{{value.text}}
</option>
</select>
As kludge, one can always move the name attribute of the select element to a hidden input element:
<select ng-model=“selectedValue” ng-options=“value.text for value in Model.Values”>
</select>
<input type=“hidden” name=“value” value=“{{selectedValue}}” />

You can do this:
<select ng-model="model">
<option value="">Select</option>
<option ng-repeat="obj in array" value="{{obj.id}}">{{obj.name}}</option>
</select>
-- UPDATE
After some updates, user frm.adiputra's solution is much better. Code:
obj = { '1': '1st', '2': '2nd' };
<select ng-options="k as v for (k,v) in obj"></select>

I have struggled with this problem for a while today. I read through the AngularJS documentation, this and other posts and a few of blogs they lead to. They all helped me grock the finer details, but in the end this just seems to be a confusing topic. Mainly because of the many syntactical nuances of ng-options.
In the end, for me, it came down to less is more.
Given a scope configured as follows:
//Data used to populate the dropdown list
$scope.list = [
{"FirmnessID":1,"Description":"Soft","Value":1},
{"FirmnessID":2,"Description":"Medium-Soft","Value":2},
{"FirmnessID":3,"Description":"Medium","Value":3},
{"FirmnessID":4,"Description":"Firm","Value":4},
{"FirmnessID":5,"Description":"Very Firm","Value":5}];
//A record or row of data that is to be save to our data store.
//FirmnessID is a foreign key to the list specified above.
$scope.rec = {
"id": 1,
"FirmnessID": 2
};
This is all I needed to get the desired result:
<select ng-model="rec.FirmnessID"
ng-options="g.FirmnessID as g.Description for g in list">
<option></option>
</select>
Notice I did not use track by. Using track by the selected item would alway return the object that matched the FirmnessID, rather than the FirmnessID itself. This now meets my criteria, which is that it should return a numeric value rather than the object, and to use ng-options to gain the performance improvement it provides by not creating a new scope for each option generated.
Also, I needed the blank first row, so I simply added an <option> to the <select> element.
Here is a Plunkr that shows my work.

Instead of using the new 'track by' feature you can simply do this with an array if you want the values to be the same as the text:
<select ng-options="v as v for (k,v) in Array/Obj"></select>
Note the difference between the standard syntax, which will make the values the keys of the Object/Array, and therefore 0,1,2 etc. for an array:
<select ng-options"k as v for (k,v) in Array/Obj"></select>
k as v becomes v as v.
I discovered this just based on common sense looking at the syntax.
(k,v) is the actual statement that splits the array/object into key value pairs.
In the 'k as v' statement, k will be the value, and v will be the text option displayed to the user. I think 'track by' is messy and overkill.

This was best suited for all scenarios according to me:
<select ng-model="mySelection.value">
<option ng-repeat="r in myList" value="{{r.Id}}" ng-selected="mySelection.value == r.Id">{{r.Name}}
</option>
</select>
where you can use your model to bind the data. You will get the value as the object will contain and the default selection based on your scenario.

This is how I resolved this. I tracked the select by value and set the selected item property to the model in my JavaScript code.
Countries =
[
{
CountryId = 1, Code = 'USA', CountryName = 'United States of America'
},
{
CountryId = 2, Code = 'CAN', CountryName = 'Canada'
}
]
<select ng-model="vm.Enterprise.AdminCountry" ng-options="country.CountryName for country in vm.Countries track by country.CountryId">
vm is my controller and the Country in the controller retrieved from the service is {CountryId =1, Code = 'USA', CountryName='United States of America'}.
When I selected another country from the select dropdown and posted my page with "Save", I got the correct country bound.

The ng-options directive does not set the value attribute on the <options> elements for arrays:
Using limit.value as limit.text for limit in limits means:
set the <option>'s label as limit.text
save the limit.value value into the select's ng-model
See Stack Overflow question AngularJS ng-options not rendering values.

You can use ng-options to achieve select tag binding to value and display members
While using this data source
countries : [
{
"key": 1,
"name": "UAE"
},
{
"key": 2,
"name": "India"
},
{
"key": 3,
"name": "OMAN"
}
]
you can use the below to bind your select tag to value and name
<select name="text" ng-model="name" ng-options="c.key as c.name for c in countries"></select>
it works great

<select ng-model="color" ng-options="(c.name+' '+c.shade) for c in colors"></select><br>

A year after the question, I had to find an answer for this question as non of these gave the actual answer, at least to me.
You have asked how to select the option, but nobody has said that these two things are NOT the same:
If we have an options like this:
$scope.options = [
{ label: 'one', value: 1 },
{ label: 'two', value: 2 }
];
And we try to set a default option like this:
$scope.incorrectlySelected = { label: 'two', value: 2 };
It will NOT work, but if you try to select the option like this:
$scope.correctlySelected = $scope.options[1];
It will WORK.
Even though these two objects have the same properties, AngularJS is considering them as DIFFERENT because AngularJS compares by the reference.
Take a look at the fiddle http://jsfiddle.net/qWzTb/.

The correct answer to this question has been provided by user frm.adiputra, as currently this seems to be the only way to explicitly control the value attribute of the option elements.
However, I just wanted to emphasize that "select" is not a keyword in this context, but it is just a placeholder for an expression. Please refer to the following list, for the definition of the "select" expression as well as other expressions that can be used in ng-options directive.
The use of select as it is depicted in the question:
ng-options='select p.text for p in resultOptions'
is essentially wrong.
Based on the list of expressions, it seems that trackexpr may be used to specify the value, when options are given in an array of objects, but it has been used with grouping only.
From AngularJS' documentation for ng-options:
array / object: an expression which evaluates to an array / object to
iterate over.
value: local variable which will refer to each item in
the array or each property value of object during iteration.
key: local variable which will refer to a property name in object during
iteration.
label: The result of this expression will be the label for
element. The expression will most likely refer to the value
variable (e.g. value.propertyName).
select: The result of this expression will be bound to the model of the parent element.
If not specified, select expression will default to value.
group: The result of this expression will be used to group options using the DOM
element.
trackexpr: Used when working with an array of objects. The result of this expression will be used
to identify the objects in the array. The trackexpr will most likely refer to the
value variable (e.g. value.propertyName).

Selecting an item in ng-options can be a bit tricky depending on how you set the data source.
After struggling with them for a while I ended up making a sample with most common data sources I use. You can find it here:
http://plnkr.co/edit/fGq2PM?p=preview
Now to make ng-options work, here are some things to consider:
Normally you get the options from one source and the selected value from other. For example:
states :: data for ng-options
user.state :: Option to set as selected
Based on 1, the easiest/logical thing to do is to fill the select with one source and then set the selected value trough code. Rarely would it be better to get a mixed dataset.
AngularJS allows select controls to hold more than key | label. Many online examples put objects as 'key', and if you need information from the object set it that way, otherwise use the specific property you need as key. (ID, CODE, etc.. As in the plckr sample)
The way to set the value of the dropdown/select control depends on #3,
If the dropdown key is a single property (like in all examples in the plunkr), you just set it, e.g.:
$scope.dropdownmodel = $scope.user.state;
If you set the object as key, you need to loop trough the options, even assigning the object will not set the item as selected as they will have different hashkeys, e.g.:
for (var i = 0, len = $scope.options.length; i < len; i++) {
if ($scope.options[i].id == savedValue) { // Your own property here:
console.log('Found target! ');
$scope.value = $scope.options[i];
break;
}
}
You can replace savedValue for the same property in the other object, $scope.myObject.myProperty.

For me the answer by Bruno Gomes is the best answer.
But actually, you need not worry about setting the value property of select options. AngularJS will take care of that. Let me explain in detail.
Please consider this fiddle
angular.module('mySettings', []).controller('appSettingsCtrl', function ($scope) {
$scope.timeFormatTemplates = [{
label: "Seconds",
value: 'ss'
}, {
label: "Minutes",
value: 'mm'
}, {
label: "Hours",
value: 'hh'
}];
$scope.inactivity_settings = {
status: false,
inactive_time: 60 * 5 * 3, // 15 min (default value), that is, 900 seconds
//time_format: 'ss', // Second (default value)
time_format: $scope.timeFormatTemplates[0], // Default seconds object
};
$scope.activity_settings = {
status: false,
active_time: 60 * 5 * 3, // 15 min (default value), that is, 900 seconds
//time_format: 'ss', // Second (default value)
time_format: $scope.timeFormatTemplates[0], // Default seconds object
};
$scope.changedTimeFormat = function (time_format) {
'use strict';
console.log('time changed');
console.log(time_format);
var newValue = time_format.value;
// do your update settings stuffs
}
});
As you can see in the fiddle output, whatever you choose for select box options, it is your custom value, or the 0, 1, 2 auto generated value by AngularJS, it does not matter in your output unless you are using jQuery or any other library to access the value of that select combo box options and manipulate it accordingly.

Please use track by property which differentiate values and labels in select box.
Please try
<select ng-options="obj.text for obj in array track by obj.value"></select>
which will assign labels with text and value with value(from the array)

For an object:
<select ng-model="mySelect" ng-options="key as value for (key, value) in object"></select>

It is always painful for developers to with ng-options. For example: Getting an empty/blank selected value in the select tag. Especially when dealing with JSON objects in ng-options, it becomes more tedious. Here I have done some exercises on that.
Objective: Iterate array of JSON objects through ng-option and set selected first element.
Data:
someNames = [{"id":"1", "someName":"xyz"}, {"id":"2", "someName":"abc"}]
In the select tag I had to show xyz and abc, where xyz must be selected without much effort.
HTML:
<pre class="default prettyprint prettyprinted" style=""><code>
<select class="form-control" name="test" style="width:160px" ng-options="name.someName for name in someNames" ng-model="testModel.test" ng-selected = "testModel.test = testModel.test || someNames[0]">
</select>
</code></pre>
By above code sample, you might get out of this exaggeration.
Another reference:

The tutorial ANGULAR.JS: NG-SELECT AND NG-OPTIONS helped me solve the problem:
<select id="countryId"
class="form-control"
data-ng-model="entity.countryId"
ng-options="value.dataValue as value.dataText group by value.group for value in countries"></select>

<select ng-model="output">
<option ng-repeat="(key,val) in dictionary" value="{{key}}">{{val}}</option>
</select>

Run the code snippet and see the variations. Here is note for quick understanding
Example 1(Object selection):- ng-option="os.name for os in osList track by os.id". Here track by os.id is important & should be there and os.id as should NOT have before os.name.
The ng-model="my_os" should set to an object with key as id like my_os={id: 2}.
Example 2(Value selection) :- ng-option="os.id as os.name for os in osList". Here track by os.id should NOT be there and os.id as should be there before os.name.
The ng-model="my_os" should set to a value like my_os= 2
Rest code snippet will explain.
angular.module('app', []).controller('ctrl', function($scope, $timeout){
//************ EXAMPLE 1 *******************
$scope.osList =[
{ id: 1, name :'iOS'},
{ id: 2, name :'Android'},
{ id: 3, name :'Windows'}
]
$scope.my_os = {id: 2};
//************ EXAMPLE 2 *******************
$timeout(function(){
$scope.siteList = [
{ id: 1, name: 'Google'},
{ id: 2, name: 'Yahoo'},
{ id: 3, name: 'Bing'}
];
}, 1000);
$scope.my_site = 2;
$timeout(function(){
$scope.my_site = 3;
}, 2000);
})
fieldset{
margin-bottom: 40px;
}
strong{
color:red;
}
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.10/angular.min.js"></script>
<div ng-app="app" ng-controller="ctrl">
<!--//************ EXAMPLE 1 *******************-->
<fieldset>
<legend>Example 1 (Set selection as <strong>object</strong>)</legend>
<select ng-model="my_os" ng-options="os.name for os in osList track by os.id">
<option value="">--Select--</option>
</select>
{{my_os}}
</fieldset>
<!--//************ EXAMPLE 2 *******************-->
<fieldset>
<legend>Example 2 (Set selection as <strong>value</strong>. Simulate ajax)</legend>
<select ng-model="my_site" ng-options="site.id as site.name for site in siteList">
<option value="">--Select--</option>
</select>
{{my_site}}
</fieldset>
</div>

Like many said before, if I have data something like this:
countries : [
{
"key": 1,
"name": "UAE"
},
{
"key": 2,
"name": "India"
},
{
"key": 3,
"name": "OMAN"
}
]
I would use it like:
<select
ng-model="selectedCountry"
ng-options="obj.name for obj in countries">
</select>
In your Controller you need to set an initial value to get rid of the first empty item:
$scope.selectedCountry = $scope.countries[0];
// You need to watch changes to get selected value
$scope.$watchCollection(function() {
return $scope.selectedCountry
}, function(newVal, oldVal) {
if (newVal === oldVal) {
console.log("nothing has changed " + $scope.selectedCountry)
}
else {
console.log('new value ' + $scope.selectedCountry)
}
}, true)

Here is how I solve this problem in a legacy application:
In HTML:
ng-options="kitType.name for kitType in vm.kitTypes track by kitType.id" ng-model="vm.itemTypeId"
In JavaScript:
vm.kitTypes = [
{"id": "1", "name": "Virtual"},
{"id": "2", "name": "Physical"},
{"id": "3", "name": "Hybrid"}
];
...
vm.itemTypeId = vm.kitTypes.filter(function(value, index, array){
return value.id === (vm.itemTypeId || 1);
})[0];
My HTML displays the option value properly.

ngOptions directive:
$scope.items = [{name: 'a', age: 20},{ name: 'b', age: 30},{ name: 'c', age: 40}];
Case-1) label for value in array:
<div>
<p>selected item is : {{selectedItem}}</p>
<p> age of selected item is : {{selectedItem.age}} </p>
<select ng-model="selectedItem" ng-options="item.name for item in items">
</select>
</div>
Output Explanation (Assume 1st item selected):
selectedItem = {name: 'a', age: 20} // [by default, selected item is equal to the value item]
selectedItem.age = 20
Case-2) select as label for value in array:
<div>
<p>selected item is : {{selectedItem}}</p>
<select ng-model="selectedItem" ng-options="item.age as item.name for item in items">
</select>
</div>
Output Explanation (Assume 1st item selected):
selectedItem = 20 // [select part is item.age]

Get name of field being passed

I have two sets of lists (state lists)
One called state_o and one called state_d and I have a function I do on them
function selectCountry(sel) {
document.getElementById("country_o").selectedIndex = states[sel.value];
}
Now what I want to do is determine if the "sel" is state_o or state_d and change the getElementById("country_o") to either _o or _d depending on what state is selected, so state_o would do country_o and state_d would do country_d
How can I determine the select field name?
Thanks!

You can access the name property through javascript:
function selectCountry(sel) {
var od = sel.name == "state_o" ? "o" : "d";
document.getElementById("country_"+od).selectedIndex = states[sel.value];
}
Or if you want to be a bit fancier and keep it on one line, slice the o/d straight from the name string:
function selectCountry(sel) {
document.getElementById("country_"+sel.name.slice(-1)).selectedIndex = states[sel.value];
}

If I've understood your question right, it's just:
var field;
if (sel.value == 'state_o')
field = 'country_o';
else
field = 'country_d';
document.getElementById(field).selectedIndex = states[sel.value];

If sel is the select element, sel.id or sel.name should give you what you want.

Keep another parameter in this function to see if its _o or _d and set this value in calling function.
then in your javascript method you can call country by -
document.getElementById("country" + param2)
Assuming param2 is that additional parameter and it will contain string "_o" or "_d"

Use sel.attr('name') if you're using jQuery or sel.name if just using plain old Javascript
Assuming you have:
<SELECT name='state_o'>
<OPTION value='blah'>BLAH</OPTION>
</SELECT>
<SELECT name='state_d'>
<OPTION value='blah'>BLAH</OPTION>
</SELECT>