In TypeScript, a Tuple is the data structure that allows storing a fixed number of elements of different types in a specific order. We can find the length of a tuple using various approaches that are implemented in this article in terms of examples.

There are several approaches available in TypeScript for finding the length of a tuple which are as follows:

Using the length property

In this approach, we are using the length property directly on the tuple variable to obtain its length, which counts the number of elements in the tuple.

Syntax:

tuple.length 

Example: The below example uses the length property to find the length of a dictionary in TypeScript.

let tuple: [number, string, boolean] = [2009, "GFG", true];
let tupleLength = tuple.length;
console.log("Tuple Length:", tupleLength);

Output:

"Tuple Length:",  3 

Using a for…in loop

In this approach, we are using a for…in loop to iterate through the tuple and increment a counter variable (tupleLength) for each element encountered, effectively counting the number of elements in the tuple.

Syntax:

for (variable in object) {
 // code 

Example: The below example uses the for…in loop to find the length of a tuple in TypeScript.

let tuple: [number, string, boolean] = [2009, "GFG", true];
let tupleLength = 0;
for (let _ in tuple) {
    tupleLength++;
}
console.log("Tuple Length:", tupleLength);

Output:

"Tuple Length:",  3 

Using the reduce method

In this approach, we are using the reduce method to accumulate the length of the tuple by adding 1 to the accumulator (acc) for each element encountered during the reduction process.

Syntax:

array.reduce(callback: (accumulator: T, currentValue: T, currentIndex: 
number, array: T[]) => T, initialValue?: T): T; 

Example: The below example uses the reduce function to find the length of a tuple in TypeScript.

let tuple: [number, string, boolean] = [2009, "GFG", true];
let tupleLength = tuple
    .reduce((acc: number, curr: any) => acc + 1, 0);
console.log("Tuple Length:", tupleLength);

Output:

"Tuple Length:",  3 

Using TypeScript’s Type Utilities

In this approach, we will use TypeScript’s type utilities to determine the length of a tuple. This method leverages TypeScript’s type system to compute the length at compile time, ensuring type safety and potentially improving performance by avoiding runtime calculations.

Syntax:

type Length<T extends readonly any[]> = T['length'];

Example: In this example we defines a Length type utility to extract the length of a tuple. It infers the length of the tuple tuple and prints it using tuple.length

type Length<T extends readonly any[]> = T['length'];

let tuple: [number, string, boolean] = [2009, "GFG", true];
type TupleLength = Length<typeof tuple>;

console.log("Tuple Length:", tuple.length);

Output:

Tuple Length: 3

Using recursion:

In this approach, we define a recursive function that iterates through the tuple and counts the elements until reaching the end of the tuple. Recursion allows us to traverse through each element of the tuple without needing to know its length beforehand.

Example:

function tupleLength<T extends unknown[]>(tuple: T): number {
    function countElements(tuple: unknown[], index: number): number {
        if (tuple[index] !== undefined) {
            return 1 + countElements(tuple, index + 1);
        } else {
            return 0;
        }
    }
    return countElements(tuple, 0);
}
const tuple: [string, number, boolean] = ['apple', 5, true];
const length = tupleLength(tuple);

console.log("Tuple Length:", length);

Output

Tuple Length: 3