Numeric enums in Typescript

Introduction

Numeric enums let you group related numbers with names. This makes your code easier to read and understand.

When you want to name a set of related numbers, like days of the week or directions.

When you need to compare or switch between fixed numeric values with meaningful names.

When you want to avoid using 'magic numbers' directly in your code.

When you want to make your code clearer for others by using descriptive names instead of numbers.

Syntax

Typescript

enum Name {
  Member1 = 1,
  Member2,
  Member3 = 10,
  Member4
}

If you don't assign a number to the first member, it starts at 0 by default.

Members without assigned numbers get the previous member's number plus one.

Examples

Starts at 1 for Up, then Down is 2, Left is 3, Right is 4 automatically.

Typescript

enum Direction {
  Up = 1,
  Down,
  Left,
  Right
}

No numbers assigned, so Ready=0, Waiting=1, Done=2 by default.

Typescript

enum Status {
  Ready,
  Waiting,
  Done
}

Red is 5, Green is 10, Blue is 11 (one more than Green).

Typescript

enum Color {
  Red = 5,
  Green = 10,
  Blue
}

Sample Program

This program defines days Monday to Friday starting at 1. It checks if a day is weekend (6 or 7). Monday prints as 1, Wednesday as 3, and Monday is not weekend.

Typescript

enum Weekday {
  Monday = 1,
  Tuesday,
  Wednesday,
  Thursday,
  Friday
}

function isWeekend(day: Weekday): boolean {
  return day === 6 || day === 7;
}

console.log(Weekday.Monday);    // 1
console.log(Weekday.Wednesday); // 3
console.log(isWeekend(Weekday.Monday)); // false

Important Notes

Numeric enums can be used in comparisons and switch statements easily.

You can get the name from the number using reverse lookup, like Weekday[1] gives 'Monday'.

Be careful to assign numbers if you want specific values; otherwise, they auto-increment.

Summary

Numeric enums give names to numbers for clearer code.

Members auto-increment if no number is assigned.

Use enums to avoid magic numbers and improve readability.