Lesson 06 of 55
9 mins readLiteral Types, String Enums & Const Enums
In Plain English
Literal types restrict values to exact strings, numbers, or booleans (`"GET" | "POST"`). Enums allow declaring a set of named numeric or string constants.
Deep Dive: How It Works
Literal Unions: `type Method = "GET" | "POST" | "PUT" | "DELETE"`.
String Enums: `enum Direction { Up = "UP", Down = "DOWN" }`.
Const Enums: `const enum` completely inlines values during compilation without generating an object in JS output.
Union vs Enum: In modern TypeScript, string literal unions (`type Status = "idle" | "busy"`) are often preferred over enums.
Core Rules to Remember
Literal Unions Preferred: `"light" | "dark"` is lightweight, zero-runtime, and JSON compatible.
Const Enums Inline Values: `const enum` inlines constants directly into call sites for performance.
Live Interactive Example
Hit Run Code to see it liveLiteral Types and Enums
Python 3.12
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Output Console
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How it works: Theme allowed only the three exact string values, and LogLevel provided named constants.
Your Turn: Micro Challenge
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Micro Exercise
Define Action Literal Union
- Define `type ActionType = "CREATE" | "UPDATE" | "DELETE";`
- Write `function handleAction(act: ActionType): string { return "Action executed: " + act; }`
- Log `handleAction("CREATE")`.
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Sandbox Output
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