2. Tutorials
  3. Add an Item to the Beginning of an Array in JavaScript or Node.js

Add an Item to the Beginning of an Array in JavaScript or Node.js

Arrays are a commonly used data structure in JavaScript. When interacting with arrays, you likely want to manipulate them by adding new items. In some situations, you may want to add items to the beginning of an array.

This tutorial shows you three ways on how to prepend items to an array.

Node.js Series Overview

  1. Increase the Memory Limit for Your Process
  2. Why You Should Add “node” in Your Travis Config
  3. Create a PDF from HTML with Puppeteer and Handlebars
  4. Create Your Own Custom Error
  5. Retrieve a Request’s IP Address in Node.js
  6. Detect the Node.js Version in a Running Process or App
  1. String Replace All Appearances
  2. Remove All Whitespace From a String in JavaScript
  3. Generate a Random String in Node.js or JavaScript
  4. Remove Extra Spaces From a String in JavaScript or Node.js
  5. Remove Numbers From a String in JavaScript or Node.js
  6. Get the Part Before a Character in a String in JavaScript or Node.js
  7. Get the Part After a Character in a String in JavaScript or Node.js
  8. How to Check if a Value is a String in JavaScript or Node.js
  9. Check If a String Includes All Strings in JavaScript/Node.js/TypeScript
  10. Check if a Value is a String in JavaScript and Node.js
  11. Limit and Truncate a String to a Given Length in JavaScript and Node.js
  12. Split a String into a List of Characters in JavaScript and Node.js
  1. Filter Data in Streams
  1. Get Number of Seconds Since Epoch in JavaScript
  2. Get Tomorrow’s Date in JavaScript
  3. Increase a Date in JavaScript by One Week
  4. Add Seconds to a Date in Node.js and JavaScript
  5. Add Month(s) to a Date in JavaScript or Node.js
  6. Add Week(s) to a Date in JavaScript or Node.js
  1. How to Run an Asynchronous Function in Array.map()
  2. How to Reset and Empty an Array
  3. for…of vs. for…in Loops
  4. Clone/Copy an Array in JavaScript and Node.js
  5. Get an Array With Unique Values (Delete Duplicates)
  6. Sort an Array of Integers in JavaScript and Node.js
  7. Sort a Boolean Array in JavaScript, TypeScript, or Node.js
  8. Check If an Array Contains a Given Value in JavaScript or Node.js
  9. Add an Item to the Beginning of an Array in JavaScript or Node.js
  10. Append an Item at the End of an Array in JavaScript or Node.js
  11. How to Exit and Stop a for Loop in JavaScript and Node.js
  12. Split an Array Into Smaller Array Chunks in JavaScript and Node.js
  13. How to Get an Index in a for…of Loop in JavaScript and Node.js
  14. How to Exit, Stop, or Break an Array#forEach Loop in JavaScript or Node.js
  15. Retrieve a Random Item From an Array in JavaScript or Node.js
  1. Callback and Promise Support in your Node.js Modules
  2. Run Async Functions/Promises in Sequence
  3. Run Async Functions/Promises in Parallel
  4. Run Async Functions in Batches
  5. How to Fix “Promise resolver undefined is not a function” in Node.js or JavaScript
  6. Detect if Value Is a Promise in Node.js and JavaScript
  1. Human-Readable JSON.stringify() With Spaces and Line Breaks
  2. Write a JSON Object to a File
  3. Create a Custom “toJSON” Function in Node.js and JavaScript
  1. Check If a Value Is Iterable in JavaScript or Node.js
  1. Extend Multiple Classes (Multi Inheritance)
  2. Retrieve the Class Name at Runtime in JavaScript and Node.js
  1. Generate a Random Number in Range With JavaScript/Node.js
  2. Ensure a Positive Number in JavaScript or Node.js
  1. How to Merge Objects
  2. How to Check if an Object is Empty in JavaScript or Node.js
  3. How to CamelCase Keys of an Object in JavaScript or Node.js
  4. How to Snake_Case Keys of an Object in JavaScript or Node.js
  5. How to Destructure a Dynamic Key in JavaScript or Node.js
  1. Get a File’s Created Date
  2. Get a File’s Last Modified/Updated Date
  3. How to Create an Empty File
  4. Check If a Path or File Exists
  5. How to Rename a File
  6. Check If a Path Is a Directory
  7. Check If a Path Is a File
  8. Retrieve the Path to the User’s Home Directory
  9. How to Touch a File
  10. Read File Content as String
  11. Check If a Directory Is Empty
  1. Create From Object
  2. Transform to an Object
  1. Determine the Node.js Version Running Your Script

3 Ways Adding Items to the Beginning of a JavaScript Array

JavaScript supports different ways of adding items to the beginning of an array. You can use the native Array#unshift method, create a new array in combination with spreading existing items into the new array or create a new array by concatenating two arrays.

Prepend Items to an Existing Array

The Array#unshift method adds one or more items to the beginning of an array.

Notice: Array#unshift returns the new length of the array, not the array containing the new item(s):

const ids = [1, 2]

const newArrayLength = ids.unshift(3)  
// 3
// the value of "ids" is [3, 1, 2]

ids.unshift(4)  
// the value of "ids" is [4, 3, 1, 2]

// or prepend multiple values

ids.unshift(5, 6, 7)  
// the value of "ids" is [5, 6, 7, 4, 3, 1, 2]

Add and Spread Items Into a New Array

You can also create a new array and add the new items at the beginning. This is a short and concise way in combination with the spread operator to add the values of an existing array:

const ids = [1, 2, 3]

const newIds = [4, ...ids]  
// [4, 1, 2, 3]

const newIds = [4, 5, 6, ...ids]  
// [4, 5, 6, 1, 2, 3]

Concat(enate) Arrays Items

You may also create a new array of the items you want to prepend to the existing array. Then, concatenate the existing items to the end of the new array. This keeps the new items in the front and appends the existing ones to the end:

const ids = [1, 2, 3]

const newIds = [4, 5, 6].concat(ids)  
// the value of "newIds" is [4, 5, 6, 1, 2, 3]

All three ways allow you to prepend one or more items to the beginning of an array. Enjoy!

What Should You Use?

Well, use what you like best!

I prefer Array#concat when building an array pipeline by chaining further operations, like Array#map, Array#filter, or Array#find.

In situations where I only want to prepend the item without additional operations, I’m using the spread operator.

In terms of performance: I don’t really care about performance optimizations on my side. I’m relying on the JavaScript runtime to optimize the code for me. This gives me the freedom of writing the code I like to read 😃

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.

Explore the Library

Find interesting tutorials and solutions for your problems.

Android

Node.js

Server

Miscellaneous