Enumerations

const myEnum = { 
   Up : 'Up string', 
   Down : 'Down string', 
   Right : 'Right string', 
   Left : 'Left string' 
} 

let myValue: number = myEnum.Up; 

Returns an array

Object.keys(myEnum) 

Check if a value equals

=== myEnum.Down 

Check if a value is in the enumeration

myEnum.hasOwnProperty('Up');  

Object.Freeze

However it is possible in your code to redefine these constants

myEnum.Up = 'change the text'; 

To prevent the value from being changed we can freeze the enumeration

const myEnum = Object.freeze({ 
   Up : 'Up string', 
   Down : 'Down string', 
   Right : 'Right string', 
   Left : 'Left string' 
}); 

Type Literals

Do not use enums, just use type literals ?

type Colors = 'red | 'blue' | 'green'  

TypeScript Enumerations

At the moment the "enum" keyword has not been added to JavaScript
TypeScript Enumerations