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Split an Array Into Smaller Array Chunks in JavaScript and Node.js

We recently ran into a problem with a large array. The number of items in the array was too large to process them at once. We wanted to offload smaller chunks of these items to a queue worker.

This tutorial shows you how to split an array into a list of smaller chunks.

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Divide and Chunk an Array Into Smaller Arrays

This approach of dividing an array into smaller chunks assumes a fixed chunk size. For example, we want to split the array [1, 2, 3, 4, 5, 6, 7, 8] into chunks of three items. The result of chunking the source array should look like this:

[
  [1, 2, 3],
  [4, 5, 6],
  [7, 8]
]

JavaScript comes with the Array#splice method. The splice method removes items from an array and returns them as a new array. This way, you can remove the number of items from the source array until it’s empty.

Here’s a sample implementation for a chunk(items, size) function:

/**
 * Split the `items` array into multiple, smaller arrays of the given `size`.
 *
 * @param {Array} items
 * @param {Number} size
 *
 * @returns {Array[]}
 */
function chunk (items, size) {  
  const chunks = []
  items = [].concat(...items)

  while (items.length) {
    chunks.push(
      items.splice(0, size)
    )
  }

  return chunks
}

// Example

const items = [1, 2, 3, 4, 5, 6, 7, 8]

chunk(items, 3)  
// [ [1, 2, 3], [4, 5, 6], [7, 8] ]

The basic idea of this function is to remove items from the source array and push the removed elements array to the result array. The result contains all smaller chunks for further processing.

Use the @supercharge/collections Package

I’m the maintainer of the @supercharge/collections package providing convenient array utilities. This package comes with the .chunk(<size>) method splitting the given array into arrays of the given size.

Wrapping an array using the @supercharge/collections package creates a collection instance. You must end the chain with .all() to retrieve the underlying JavaScript array:

const Collect = require('@supercharge/collections')

Collect([1, 2, 3, 4, 5, 6, 7, 8]).chunk(3).all()  
// [ [1, 2, 3], [4, 5, 6], [7, 8] ]

Collect([1, 2, 3, 4, 5, 6, 7, 8]).chunk(15).all()  
// [ [1, 2, 3, 4, 5, 6, 7, 8] ]

Enjoy!

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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