To get the first N number of elements from an array in JavaScript, there are several approaches that can be taken. Here are a few:
- Using the slice() Method
- Using a for loop
- Using the splice() Method
- Using the filter() Method
Example 1: Input: arr = [1, 2, 3, 4, 5, 6], n = 3 Output: [1, 2, 3] Example 2: Input: arr = [6, 1, 4, 9, 3, 5, 7], n = 4 Output: [6, 1, 4, 9]
Method 1: Using the slice() method
The slice() method is used to extract a part of an array and returns a new array containing the extracted elements. It does not change the original array.
Syntax:
array.slice(start, end);
Here, start is the starting index from where to begin extraction and end is the ending index from where to end extraction. The end index is exclusive, i.e., the element at the end index is not included in the extracted array.
Example 1:
Javascript
const arr = [1, 2, 3, 4, 5, 6]; const n = 3; const result = arr.slice(0, n); console.log(result); // Output: [1, 2, 3] |
[ 1, 2, 3 ]
In the above example, we have an array arr and we want to extract the first 3 elements from it. So, we used the slice() method with a start index of 0 and an end index of 3, which extracts the first 3 elements.
Example 2:
Javascript
const arr = ['apple', 'banana', 'orange', 'grape', 'kiwi']; const n = 2; const result = arr.slice(0, n); console.log(result); // Output: ['apple', 'banana'] |
[ 'apple', 'banana' ]
In the above example, we have an array arr and we want to extract the first 2 elements from it. So, we used the slice() method with a start index of 0 and an end index of 2 to extract the first 2 elements.
Method 2: Using a for loop
We can also use a for loop to iterate through the array and extract the first N elements.
Syntax:
for (let i = 0; i < n; i++) {
// Access and store elements here
}
Example 1:
Javascript
const arr = [1, 2, 3, 4, 5, 6]; const n = 3; // Number of elements to extract const result = []; for (let i = 0; i < n; i++) { result.push(arr[i]); } console.log(result); // Output: [1, 2, 3] |
[ 1, 2, 3 ]
In the above example, we have initialized an empty array result and used a for loop to iterate through the first n elements of the original array arr. We accessed and stored the elements in the result array.
Example 2:
Javascript
const arr = ['apple', 'banana', 'orange', 'grape', 'kiwi']; const n = 3; const result = []; for (let i = 0; i < n && i < arr.length; i++) { result.push(arr[i]); } console.log(result); // Output: ['apple', 'banana', 'orange'] |
[ 'apple', 'banana', 'orange' ]
In the above example, we declare an empty array result to store the extracted elements. Then, we use a for loop to iterate over the elements of the original array arr and push the first n elements to the result array using the push() method. The loop condition is set to terminate when either n elements have been extracted or all the elements of the original array have been processed.
Method 3: Using the splice() method
The splice() method can be used to add or remove elements from an array. We can use it to remove all elements after the first N elements.
Syntax:
array.splice(start, deleteCount);
Here, start is the starting index from where to begin deletion, and deleteCount is the number of elements to be deleted. We can set deleteCount to the length of the array to remove all elements after the first N elements.
Example 1:
Javascript
const arr = [1, 2, 3, 4, 5, 6]; const n = 3; arr.splice(n); console.log(arr); // Output: [1, 2, 3] |
[ 1, 2, 3 ]
In the above example, we have an array arr and we want to remove all elements after the first 3 elements. So, we used the splice() method with start index 3 (which is the index of the fourth element) and deleteCount set to the length of the array minus N.
Example 2:
Javascript
const arr = ['apple', 'banana', 'orange', 'grape', 'kiwi']; const n = 3; arr.splice(n); console.log(arr); // Output: ['apple', 'banana', 'orange'] |
[ 'apple', 'banana', 'orange' ]
In the above example, we have an array arr and we want to remove all elements after the first 3 elements. So, we used the splice() method with start index 3 (which is the index of the fourth element) and deleteCount set to the length of the array minus N.
Method 4: Using the filter() method
We can also use the filter() method but this method is not much efficient because it iterates over the entire array.
Example:
Javascript
const arr = [1,2,3,4,5,6]; const n = 4; const newArray = arr.filter((element, index) => index < n); console.log(newArray); |
Output:
[ 1, 2, 3, 4 ]
