Enumerated Types in Typescript

Question

Enumerated Types in Typescript

Although this question has been asked multiple times, I am still struggling to grasp the concept of enums.
Let's consider a simple enum:

export enum Type { 
  Null,
  First, 
  Second,
  Third
}

Now, the query is, what is the difference between these code snippets?

if (myObject.type === 2) doStuff();

And this one:

if (myObject.type === Type.Second) doStuff();

I retrieve myObject from the backend and need to identify its type to execute specific functions. Why should I use enums in this scenario?
I might be mistaken, but both examples seem to achieve the same outcome.
Could you please clarify why I should incorporate enums in my use case?

angular typescript enums

Answer 1

Answer №1

It's true that in pure Javascript, both functions perform identically. However, TypeScript provides an added layer of security for potential changes in your code down the line.

Consider a scenario where you introduce a new element to your enum. Let's say you insert a zero-index element between null and first. As a result, Type.Second will now have a value of 3, rendering your original check for === 2 incorrect. Consistently utilizing enums can help prevent these types of future mistakes.

Answer 2

It's true that in pure Javascript, both functions perform identically. However, TypeScript provides an added layer of security for potential changes in your code down the line.

Consider a scenario where you introduce a new element to your enum. Let's say you insert a zero-index element between null and first. As a result, Type.Second will now have a value of 3, rendering your original check for === 2 incorrect. Consistently utilizing enums can help prevent these types of future mistakes.

Answer 3

Answer №2

Both snippets of code perform similar functions. The Type.Second will hold the number linked to the enum member, while type (assuming it is defined as Type) should store an enum member and thus should translate to a number during runtime. This implies that in both scenarios, numbers are being compared; the only difference is that in the second case, the value is embedded within the code, whereas in the first case, it is retrieved through accessing an object's member.

In situations where the server does not return numbers but rather returns the name of the enum, neither approach will yield the expected outcome.

It is important to remember that although not recommended, it is possible to alter the runtime values of the enum object, which may lead to unforeseen consequences:

(Type as any)["Second"] = 10

If you desire complete uniformity between the two cases (i.e., identical compiled code), employing a const enum can achieve this. const enums do not rely on a runtime object; instead, all references to members are substituted with the actual value of the enum:

export const enum Type { 
  Null,
  First, 
  Second,
  Third
}

if (myObject.type === Type.Second) doStuff();
// Transforms to 

if (myObject.type === 2 /* Second */)
    doStuff

Answer 4

Both snippets of code perform similar functions. The Type.Second will hold the number linked to the enum member, while type (assuming it is defined as Type) should store an enum member and thus should translate to a number during runtime. This implies that in both scenarios, numbers are being compared; the only difference is that in the second case, the value is embedded within the code, whereas in the first case, it is retrieved through accessing an object's member.

In situations where the server does not return numbers but rather returns the name of the enum, neither approach will yield the expected outcome.

It is important to remember that although not recommended, it is possible to alter the runtime values of the enum object, which may lead to unforeseen consequences:

(Type as any)["Second"] = 10

If you desire complete uniformity between the two cases (i.e., identical compiled code), employing a const enum can achieve this. const enums do not rely on a runtime object; instead, all references to members are substituted with the actual value of the enum:

export const enum Type { 
  Null,
  First, 
  Second,
  Third
}

if (myObject.type === Type.Second) doStuff();
// Transforms to 

if (myObject.type === 2 /* Second */)
    doStuff

Answer 5

Answer №3

Have you ever considered examining the compiled javascript of your enum in typescript?

export enum Type { 
  Null,
  First, 
  Second,
  Third
}

When compiled, it looks something like this:

var Type = {};
Type[Type["Null"] = 0] = "Null";
Type[Type["First"] = 1] = "First";
Type[Type["Second"] = 2] = "Second";
Type[Type["Third"] = 3] = "Third";

Give it a try in the playground

Therefore, it's clear that accessing Type.Second will give you the number 2, and using Type[2] will return "Second".

Could you elaborate on why I should utilize enums in my scenario?

There are several compelling reasons to consider:

Enums make your code more readable.
Your code won't break if someone makes changes to the enum values:

export enum Type { 
    Null,
    First, 
    Second = 3, /// now it's 3
    Third
}

export enum Type { 
    Undefined, /// This is 0
    Null, /// 1
    First, /// 2
    Second, /// 3
    Third
}

This leads to more reliable and maintainable code in the long run.

Answer 6

Have you ever considered examining the compiled javascript of your enum in typescript?

export enum Type { 
  Null,
  First, 
  Second,
  Third
}

When compiled, it looks something like this:

var Type = {};
Type[Type["Null"] = 0] = "Null";
Type[Type["First"] = 1] = "First";
Type[Type["Second"] = 2] = "Second";
Type[Type["Third"] = 3] = "Third";

Give it a try in the playground

Therefore, it's clear that accessing Type.Second will give you the number 2, and using Type[2] will return "Second".

Could you elaborate on why I should utilize enums in my scenario?

There are several compelling reasons to consider:

Enums make your code more readable.
Your code won't break if someone makes changes to the enum values:

export enum Type { 
    Null,
    First, 
    Second = 3, /// now it's 3
    Third
}

export enum Type { 
    Undefined, /// This is 0
    Null, /// 1
    First, /// 2
    Second, /// 3
    Third
}

This leads to more reliable and maintainable code in the long run.

Enumerated Types in Typescript

Answer №1

Answer №2

Answer №3

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