如何在对象的开头添加元素

Question

I have an object:

TICKET_PRIORITIES: {
    LOW: 'low',
    NORMAL: 'normal',
    HIGH: 'high',
    VERY_HIGH: 'very high'
}

In client side I have to add select at first.

Result I wanted to be

TICKET_PRIORITIES: {
    SELECT: 'select',    
    LOW: 'low',
    NORMAL: 'normal',
    HIGH: 'high',
    VERY_HIGH: 'very high'
}

<select ng-model="selectedPriority" ng-options="key as key | translate for (key, value) in priorities" class="form-control m-b"> </select> 

In this select I wanna select "select" option and select option should be at the first of drop down.

Answer 1

var TICKET_PRIORITIES = {
    LOW: 'low',
    NORMAL: 'normal',
    HIGH: 'high',
    VERY_HIGH: 'very high'
  };
TICKET_PRIORITIES['SELECT']='select';
alert(JSON.stringify(TICKET_PRIORITIES));  

Demo

Answer 2

Object properties order are not concerned while creating object but you can create new properties like:

TICKET_PRIORITIES = {
    LOW: 'low',
    NORMAL: 'normal',
    HIGH: 'high',
    VERY_HIGH: 'very high'
  }

TICKET_PRIORITIES.SELECT='select';

Answer 3

This is not possible . Javascript does not care about or enforce the order of properties in objects (see this question for reference). Or, to quote the ECMAscript standard (emphasis mine):

4.3.3 Object An object is a member of the type Object. It is an unordered collection of properties each of which contains a primitive value, object, or function. A function stored in a property of an object is called a method.

If order is important to you, you will need a different data structure using arrays, eg something like this:

TICKET_PRIORITIES: [
    {id: "LOW", label: "low"},
    {id: "NORMAL", label: "normal"},
    {id: "HIGH", label: "high"},
    {id: "VERY_HIGH", label: "very high"}
]

This allows you to do something like this ( unshift adds an element to the beginng of an array):

TICKET_PRIORITIES.unshift({id: "SELECT", label: "select"})