Enum member access in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an enum in TypeScript?

An enum is a way to define a set of named constants. It helps group related values under one name for easier use and better code clarity.

beginner

How do you access a numeric enum member by its name?

You use dot notation with the enum name and member name, like EnumName.MemberName.

intermediate

How can you get the name of an enum member from its numeric value?

TypeScript enums create a reverse mapping, so you can use EnumName[value] to get the member name as a string.

beginner

What happens if you try to access an enum member that does not exist?

You get undefined because the member name or value is not found in the enum.

intermediate

Can you access enum members using variables? How?

Yes, you can use bracket notation with a variable holding the member name or value, like EnumName[variable].

How do you access the enum member 'Red' in enum Color { Red, Green, Blue }?

A Red.Color

B Color.Red

C Color->Red

D Color['Red']()

You access enum members using dot notation: Color.Red.

What does Color[0] return if enum Color { Red, Green, Blue }?

A 'Green'

B 0

C 'Red'

D undefined

Numeric enums have reverse mapping, so Color[0] returns the member name 'Red'.

If you try Color['Yellow'] and 'Yellow' is not a member, what is the result?

A Throws error

B null

C Returns 'Yellow'

D undefined

Accessing a non-existent enum member returns undefined.

Can you use a variable to access an enum member dynamically?

A Yes, using bracket notation like Color[varName]

B No, only dot notation works

C Yes, but only with string enums

D No, enums are static

Bracket notation allows dynamic access using variables.

What type of enum member access allows getting the member name from its value?

A Reverse mapping in numeric enums

B Dot notation

C Bracket notation with string enums

D You cannot get member name from value

Numeric enums have reverse mapping to get member names from values.

Explain how to access enum members by name and by value in TypeScript.

Think about how you use the enum name and member name or value.

Describe what happens when you try to access an enum member that does not exist.

Consider what JavaScript returns when a property is missing.