Summary  
Literal types allow you to restrict a variable to one or more exact string or number values instead of a broader type, ensuring only those specific values can be assigned and catching invalid assignments at compile time.  

General domain of usage  
Function parameters

Literal types in TypeScript allow you to specify that a variable can only have one or more exact values, rather than any value of a broader type like `string` or `number`. This restriction helps prevent errors by ensuring that only expected values are used in your code. 

// String literal type
let direction: "left" | "right" | "up" | "down";
direction = "left"; // OK
direction = "up";   // OK
// direction = "forward"; // Error: Type '"forward"' is not assignable to type '"left" | "right" | "up" | "down"'

// Number literal type
let diceRoll: 1 | 2 | 3 | 4 | 5 | 6;
diceRoll = 4; // OK
diceRoll = 6; // OK
// diceRoll = 7; // Error: Type '7' is not assignable to type '1 | 2 | 3 | 4 | 5 | 6'

In the example above, the `direction` variable is limited to four possible string values: `"left"`, `"right"`, `"up"`, or `"down"`. Any attempt to assign a different string will result in a type error. Similarly, the `diceRoll` variable can only be one of the numbers from `1` to `6`, matching the faces of a standard die. **Literal types** are especially useful for function parameters, configuration options, or any situation where only a specific set of values makes sense. By using literal types, you make your code safer, clearer, and more predictable.

Which of the following declarations use literal types in TypeScript?

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Literal Types

Literal Types