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TypeScript Inference - GeeksforGeeks

Last Updated : 21 Jan, 2025

TypeScript's type inference automatically determines the types of variables, function return values, objects, and arrays based on their assigned values and usage.

• This feature reduces the need for explicit type annotations, simplifying code while maintaining type safety.
• By analyzing the context and initial values, TypeScript ensures that variables and functions operate with consistent and expected types throughout the codebase.

let age = 25;
let name = "John";

console.log(`Age: ${age}`);
console.log(`Name: ${name}`);

In this Example,

• TypeScript infers age as a number and name as a string based on their assigned values.
• This automatic detection ensures type safety without requiring explicit annotations.

More Examples of TypeScript Inference

let x = 10; // TypeScript infers x as a number
console.log(typeof x);

In this Example,

• TypeScript infers the type of x as number based on the initial value 10.
• This ensures x can only hold numerical values, improving type safety.

Output:

number

let fruits = ["Apple", "Banana", "Cherry"]; // TypeScript infers fruits as string[]
console.log(fruits);

In this Example,

• TypeScript infers the type of fruits as an array of strings (string[]) based on the initial values.
• This prevents adding elements of other types, maintaining array consistency.

Output:

[ 'Apple', 'Banana', 'Cherry' ]

function add(a: number, b: number) {
    return a + b; // TypeScript infers the return type as number
}
console.log(add(5, 10));

In this Example,

• The add function's return type is inferred as number because it returns the sum of two numbers.
• This ensures the function always returns a numerical value, avoiding type-related errors.

Output:

15

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