Heterogeneous enums in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a heterogeneous enum in TypeScript?

A heterogeneous enum is an enum that contains both string and numeric values in its members.

intermediate

Why might you use a heterogeneous enum?

You might use a heterogeneous enum to represent values that need both numbers and strings, for example, when some values are codes and others are descriptive labels.

beginner

How do you declare a heterogeneous enum in TypeScript?

You declare it by assigning some members string values and others numeric values explicitly inside the enum block.

beginner

Example: What is the output of this enum member access?

enum Example {
  No = 0,
  Yes = "YES"
}
console.log(Example.Yes);

The output will be the string "YES" because the member Yes is assigned the string value "YES".

intermediate

Can heterogeneous enums cause any issues in TypeScript?

Yes, they can make code harder to understand and maintain because the enum members are not consistent in type, which can confuse type checking and usage.

Which of the following is a valid heterogeneous enum in TypeScript?

A enum Mixed { A = 1, B = 2 }

B enum Mixed { A, B, C }

C enum Mixed { A = "A", B = "B" }

D enum Mixed { A = 1, B = "B" }

Only option A mixes numeric and string values, making it a heterogeneous enum.

What type of values can heterogeneous enums contain?

A Both numbers and strings

B Only strings

C Only numbers

D Only booleans

Heterogeneous enums contain both numeric and string values.

What will be the output of this code?

enum Status {
  Active = 1,
  Inactive = "NO"
}
console.log(Status.Inactive);

A 1

B "NO"

C undefined

D 0

Status.Inactive is assigned the string "NO", so that is printed.

Is this enum valid?

enum Test {
  One = "1",
  Two = 2
}

A No, enums cannot mix types

B No, string values are not allowed

C Yes, it's a heterogeneous enum

D Yes, but only if all values are strings

TypeScript allows enums to mix string and numeric values, making this a valid heterogeneous enum.

What is a potential downside of using heterogeneous enums?

A They can confuse type checking and maintenance

B They are slower to compile

C They cannot be used in switch statements

D They always cause runtime errors

Mixing types in enums can make code harder to understand and maintain.

Explain what a heterogeneous enum is and give a simple example.

Think about enums that mix numbers and strings.

Describe one advantage and one disadvantage of using heterogeneous enums.

Consider why mixing types might help or hurt your code.