TypeScript Call Signatures (original) (raw)

Last Updated : 22 Jan, 2025

**TypeScript call signatures define the parameter types and return types for function-like objects, enabling the creation of callable entities with additional properties.

• Allow objects to be invoked as functions while possessing properties.
• Enhance code flexibility by combining callable behavior with structured data.

**Syntax:

type MyCallableObject = {
(parameter1: Type1, parameter2: Type2): ReturnType; // Call signature
propertyName: PropertyType; // Additional property
};

**Parameters:

• **MyCallableObject: The name of the type alias for the callable object.
• ****(parameter1: Type1, parameter2: Type2):** Defines the parameters and their types for the callable aspect.
• **ReturnType: Specifies the return type of the callable function.
• **propertyName: PropertyType: An example of an additional property within the object.

**Greeting Function Using Call Signature

TypeScript ``

type GreetingFunction = { (name: string): string; // Call signature description: string; // Additional property };

const greet: GreetingFunction = (name: string) => { return Hello, ${name}!; };

greet.description = "A function to greet users";

console.log(greet("Alice"));
console.log(greet.description);

``

• GreetingFunction defines a callable object that takes a string and returns a string.
• The greet function implements this call signature and includes an additional description property.

**Output:

Hello, Alice!
A function to greet users

Calculator Using Call Signature

TypeScript ``

type Calculator = { (a: number, b: number): number; // Call signature operation: string; // Additional property };

const add: Calculator = (a: number, b: number) => a + b; add.operation = "Addition";

const multiply: Calculator = (a: number, b: number) => a * b; multiply.operation = "Multiplication";

console.log(${add.operation}: ${add(5, 3)});
console.log(${multiply.operation}: ${multiply(5, 3)});

``

• Calculator defines a callable object that takes two number parameters and returns a number.
• The add and multiply functions implement this call signature with specific operations and include an operation property describing the operation.

**Output:

Addition: 8
Multiplication: 15

Best Practices for Using TypeScript Call Signatures

• **Clearly Define Parameter and Return Types: Ensure all call signatures specify explicit parameter and return types for better type safety.
• **Include Descriptive Properties: Add properties that provide context or metadata about the callable object to enhance code readability.
• **Use Consistent Naming Conventions: Adopt clear and consistent naming for callable objects and their properties to improve maintainability.