TypeScript Array unshift()

In this chapter, we will explore the unshift() method for arrays in TypeScript. This method is a built-in function that adds one or more elements to the beginning of an array and returns the new length of the array. Understanding how to use unshift() is useful for managing and modifying arrays, especially when you need to add elements to the start of the array.

Table of Contents

1. Definition
2. Syntax
3. Examples
4. Conclusion

1. Definition

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array. This method modifies the original array.

2. Syntax

array.unshift(element1, element2, ..., elementN);

Parameters

• element1, element2, ..., elementN: The elements to add to the beginning of the array.

Return Value

The method returns the new length of the array after the elements have been added.

3. Examples

Let's look at some examples to understand how unshift() works in TypeScript.

Example 1: Basic Usage

In this example, we use unshift() to add a single element to the beginning of an array.

let numbers: number[] = [2, 3, 4, 5];
let newLength = numbers.unshift(1);
console.log(newLength); // Output: 5
console.log(numbers);   // Output: [1, 2, 3, 4, 5]

Example 2: Adding Multiple Elements

In this example, we use unshift() to add multiple elements to the beginning of an array.

let numbers: number[] = [3, 4, 5];
let newLength = numbers.unshift(1, 2);
console.log(newLength); // Output: 5
console.log(numbers);   // Output: [1, 2, 3, 4, 5]

Example 3: Using unshift() with Strings

In this example, we use unshift() to add elements to an array of strings.

let fruits: string[] = ["banana", "mango"];
let newLength = fruits.unshift("apple", "orange");
console.log(newLength); // Output: 4
console.log(fruits);    // Output: ["apple", "orange", "banana", "mango"]

Example 4: Using unshift() with Objects

In this example, we use unshift() to add objects to an array of objects.

interface Person {
  name: string;
  age: number;
}

let people: Person[] = [
  { name: "Ankit", age: 30 },
  { name: "Priya", age: 28 }
];

let newPerson: Person = { name: "Ravi", age: 25 };
let anotherPerson: Person = { name: "John", age: 22 };
let newLength = people.unshift(newPerson, anotherPerson);
console.log(newLength); // Output: 4
console.log(people);
// Output:
// [ { name: 'Ravi', age: 25 },
//   { name: 'John', age: 22 },
//   { name: 'Ankit', age: 30 },
//   { name: 'Priya', age: 28 } ]

Example 5: Using unshift() in a Loop

In this example, we use unshift() in a loop to add elements to an array in reverse order.

let numbers: number[] = [];
for (let i = 5; i >= 1; i--) {
  numbers.unshift(i);
}
console.log(numbers); // Output: [1, 2, 3, 4, 5]

4. Conclusion

In this chapter, we explored the unshift() method for arrays in TypeScript, which is used to add one or more elements to the beginning of an array and return the new length of the array. We covered its definition, syntax, parameters, return value, and provided several examples to demonstrate its usage. Understanding how to use unshift() effectively can help in various array manipulation tasks in TypeScript, especially when managing and modifying arrays by adding elements to the beginning.