Get every Nth Element of Array using JavaScript

# Get every Nth Element of Array in JavaScript

To get every Nth element of an array:

1. Declare an empty array variable.
2. Use a for loop to iterate the array every N elements.
3. On each iteration, push the element to the new array.
4. The final array will contain every Nth element of the original array.

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function getEveryNth(arr, nth) {
  const result = [];

  for (let index = 0; index < arr.length; index += nth) {
    result.push(arr[index]);
  }

  return result;
}

// 👇️ [1, 3, 5]
console.log(getEveryNth([1, 2, 3, 4, 5, 6], 2));

// 👇️ [2, 8, 14]
console.log(getEveryNth([2, 4, 6, 8, 10, 12, 14], 3));

The function takes an array and n as parameters and returns a new array that contains every Nth element of the original array.

The first step is to declare an empty array variable that will store the results.

We used a basic for loop to iterate over the array every N elements.

On each iteration, we push the element to the results array.

By incrementing the index by n, we are able to skip the irrelevant array elements.

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function getEveryNth(arr, nth) {
  const result = [];

  for (let i = 0; i < arr.length; i += nth) {
    result.push(arr[i]);
  }

  return result;
}

Once the for loop has finished iterating, the results array contains every Nth element of the original array.

Alternatively, you can use the filter() method.

# Get every Nth Element of Array using Array.filter()

This is a two-step process:

1. Use the Array.filter() method to iterate over the array.
2. Use the current index to check if each element should be added to the new array.

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function getEveryNth(arr, nth) {
  return arr.filter((_element, index) => {
    return index % nth === 0;
  });
}

// 👇️ [1, 3, 5]
console.log(getEveryNth([1, 2, 3, 4, 5, 6], 2));

// 👇️ [2, 8, 14]
console.log(getEveryNth([2, 4, 6, 8, 10, 12, 14], 3));

The function we passed to the Array.filter() method gets called with each element in the array.

On each iteration, we use the modulo % operator to check if the remainder of dividing the current index by n is 0.

The modulo operator returns the remainder of dividing the first number by the second.

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console.log(4 % 2); // 👉️ 0
console.log(5 % 2); // 👉️ 1

The filter() method returns a new array that only contains the elements that meet the condition.

However, the filter method invokes a function for every element in the array, which is very inefficient in this scenario.

Ideally, you would want to only iterate over the array every N elements.

The for loop is more efficient because it doesn't have to loop through the entire array.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Get the first N elements of an Array in JavaScript
• Get the last N elements of an Array in JavaScript
• Get one or Multiple Random Elements from an Array in JS
• Get the First and Last Elements of an Array in JavaScript