JavaScript Array unshift() - Add Elements to Start

Introduction

The unshift() method in JavaScript is crucial when you need to add one or more elements to the beginning of an array. This method modifies the original array by inserting the new elements at the start and then shifts the existing elements to higher index positions to accommodate the new entries.

In this article, you will learn how to use the unshift() method effectively. Explore practical examples to manipulate arrays by adding elements at the beginning, and understand the implications this has on array indices and the overall array length.

Basics of unshift()

Adding a Single Element

1. Start with a simple array of elements.

2. Apply the unshift() method to add a new element at the beginning of the array.

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   let fruits = ['Apple', 'Banana'];
   fruits.unshift('Orange');
   console.log(fruits);
   

   This code adds 'Orange' to the beginning of the fruits array. The resulting array becomes ['Orange', 'Apple', 'Banana'].

Adding Multiple Elements

1. Begin with an array.

2. Use unshift() to add multiple elements at once.

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   let numbers = [2, 3, 4];
   numbers.unshift(0, 1);
   console.log(numbers);
   

   Here, 0 and 1 are added to the start of the numbers array, making the new array [0, 1, 2, 3, 4].

Advanced Usage of unshift()

Understanding Return Value

1. Recognize that unshift() returns the new length of the array after adding the elements.

2. Apply unshift() and capture the returned value to check the new array length.

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   let colors = ['Red', 'Green'];
   let newLength = colors.unshift('Blue', 'Yellow');
   console.log(newLength);  // Outputs the new length of array
   console.log(colors);
   

   The colors array now starts with 'Blue' and 'Yellow', and newLength holds the value 4, indicating the array's new length.

Implications on Array Indexes

1. Understand that all existing elements shift their indices.

2. Insert elements in an array and observe how indices of existing elements change.

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   let tools = ['Hammer', 'Screwdriver'];
   tools.unshift('Wrench');
   console.log(tools.indexOf('Hammer'));
   

   'Wrench' is added to the start, and 'Hammer's index changes from 0 to 1.

Conclusion

Utilize the unshift() method in JavaScript to add elements to the start of an array effectively. Whether adding a single item or multiple items, this method adjusts the array's indices and updates its length accordingly. Perfect for situations that require dynamic manipulation of array data, unshift() enhances flexibility in handling JavaScript arrays by allowing quick additions to the front, preparing you to manage arrays more robustly in your projects.