Heterogeneous enums in Typescript - Step-by-Step Execution

Concept Flow - Heterogeneous enums

Define enum with mixed values

↓

Assign numeric and string values

↓

Access enum members

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Use enum values in code

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Check output or behavior

This flow shows how to define an enum with both numbers and strings, then access and use its members.

Execution Sample

Typescript

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

Defines a heterogeneous enum with a number and a string, then prints both values.

Execution Table

Step	Action	Evaluation	Result
1	Define enum member No	No = 0	No assigned 0
2	Define enum member Yes	Yes = "YES"	Yes assigned "YES"
3	Access Mixed.No	Mixed.No	0
4	Access Mixed.Yes	Mixed.Yes	"YES"
5	Print Mixed.No	console.log(Mixed.No)	Outputs: 0
6	Print Mixed.Yes	console.log(Mixed.Yes)	Outputs: YES

💡 All enum members defined and accessed; program ends after printing values.

Variable Tracker

Variable	Start	After 1	After 2	Final
Mixed.No	undefined	0	0	0
Mixed.Yes	undefined	undefined	"YES"	"YES"

Key Moments - 2 Insights

Why can enum members have different types like number and string together?

Because heterogeneous enums allow mixing types, as shown in execution_table rows 1 and 2 where No is number 0 and Yes is string "YES".

Can we access enum members by their value in heterogeneous enums?

No, reverse mapping only works for numeric members. Here, Mixed.No can be reverse-mapped but Mixed.Yes cannot, as it is a string.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of Mixed.Yes at step 4?

A "YES"

B 0

C undefined

D "No"

💡 Hint

Check the 'Evaluation' and 'Result' columns at step 4 in execution_table.

At which step does the program print the numeric enum member?

A Step 6

B Step 3

C Step 5

D Step 2

💡 Hint

Look for console.log calls in execution_table rows.

If we changed Mixed.No to "NO" (a string), what would happen to reverse mapping?

A Reverse mapping would still work for No

B Reverse mapping would not work for No

C Reverse mapping would work for all members

D Reverse mapping would break the enum

💡 Hint

Recall that reverse mapping only works for numeric enum members as explained in key_moments.

Concept Snapshot

Heterogeneous enums mix numbers and strings.
Syntax: enum E { A = 1, B = "text" }
Numeric members support reverse mapping.
String members do not.
Use to represent mixed-type constants.

Full Transcript

This example shows how to create a heterogeneous enum in TypeScript with both numeric and string values. The enum Mixed has No assigned to 0 and Yes assigned to "YES". When accessing Mixed.No, it returns 0, and Mixed.Yes returns "YES". Printing these values outputs 0 and YES respectively. Reverse mapping works only for numeric members, so only Mixed.No supports it. This helps when you want enum members to have different types but still be grouped logically.