What is an Enum?

An enum is an object which has a collection of related values stored together. Javascript does not support enums. Most of the programming language like java, c, c++ supports enum and it also available with typescript too. Enums are defined using keyword enum.

How to declare an Enum?

Syntax:

enum NameofEnum {
   value1,
   value2,
    ..
}

Example: Enum

enum Directions {
North,
South,
East,
West
}

In the above example, you have defined an enum called Directions. The value given is North, South, East, West. The values are numbered from 0 for the first value in the enum and subsequently increments by 1 for the next value.

Declare An Enum with a numeric value

By default, if an enum is not given any value, it considers it a number starting from 0. Following example shows an enum with a numeric value.

enum Directions {
North = 0,
South = 1, 
East =2,
West =3
}

You may also assign a start value to the enum and the next enum values will get the incremented values. For example:

enum Directions {
North = 5,
South, // will be 6
East, // 7
West // 8
}

Now the enum value North starts with 5, so South will get value as 6, East = 7 and West = 8.

You may also assign values of your choice instead of taking the default ones. For Example:

enum Directions {
North = 5,
South = 4,
East = 6,
West = 8
}

How to access an Enum?

Following example shows how to make use of Enum in your code:

enum Directions {
    North,
    South,
    East,
    West
}

console.log(Directions.North); // output is  0
console.log(Directions["North"]); // output is 0
console.log(Directions[0]); //output is North

The compiled code to javascript is as follows:

var Directions;
(function (Directions) {
    Directions[Directions["North"] = 0] = "North";
    Directions[Directions["South"] = 1] = "South";
    Directions[Directions["East"] = 2] = "East";
    Directions[Directions["West"] = 3] = "West";
})(Directions || (Directions = {}));
console.log(Directions.North);
console.log(Directions["North"]);
console.log(Directions[0]);

Since Javascript does not support enums, it converts the enum into a self invoked functions as shown above.

Declare An Enum with a string value

You can assign string values of your choice, as shown in the example below:

Example:

enum Directions {
    North = "N",
    South = "S",
    East = "E",
    West = "W"
}

console.log(Directions.North); // output is N
console.log(Directions["North"]); // output is N
console.log(Directions[0]); // output is North

The compiled code to javascript is as follows:

var Directions;
(function (Directions) {
    Directions["North"] = "N";
    Directions["South"] = "S";
    Directions["East"] = "E";
    Directions["West"] = "W";
})(Directions || (Directions = {}));
console.log(Directions.North);
console.log(Directions["North"]);
console.log(Directions[0]);

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Reetesh Gupta

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