You’re naturally in the needs of handy utilities when working with JavaScript handling arrays. Modern JavaScript frameworks —especially the frontend frameworks— abstract most of the DOM interaction. You’re focusing on the actual logic and implement the data handling.
When implementing the logic, a handy utility related to JavaScript arrays is the ability to clone arrays. This tutorial shows you three ways using native array methods:
Array#sliceArray#concat- Spread Operator
Node.js Series Overview
- Callback and Promise Support in your Node.js Modules
- Increase the Memory Limit for Your Process
- Why You Should Add “node” in Your Travis Config
- Create a PDF from HTML with Puppeteer and Handlebars
- Create Your Own Custom Error
- Extend Multiple Classes (Multi Inheritance)
- Get a File’s Created Date
- Get a File’s Last Modified/Updated Date
- Human-Readable JSON.stringify() With Spaces and Line Breaks
- Write a JSON Object to a File
- How to Create an Empty File
- Run Async Functions/Promises in Sequence
- Run Async Functions/Promises in Parallel
- Run Async Functions in Batches
- Generate a Random Number in Range With JavaScript/Node.js
- How to Merge Objects
- How to Fix “Promise resolver undefined is not a function” in Node.js or JavaScript
- Detect if Value Is a Promise in Node.js and JavaScript
Clone an Array in JavaScript
You don’t need to iterate over the original array and push each item into another array. Cloning arrays in JavaScript is as straightforward as slice or concat.
Calling .slice on the original array clones the array:
const original = [1, 2, 3]
const clone = original.slice()
Please notice, slice creates a shallow clone, not a deep clone.
If you only want to clone a slice of the original array, you may pass the starting index as an argument to slice:
const original = [1, 2, 3]
const clone = original.slice(1)
// clone = [2, 3]
You may also use the Array#concat method for cloning:
const original = [1, 2, 3]
const clone = [].concat(original)
concat combines the two arrays and creates a new one.
Another option available in modern JavaScript and Node.js is the spread operator .... You may saw it in relation to arrays or objects. Use the spread operator to create a clone of your array by "spreading" the items of the original array into a clone:
const original = [1, 2, 3]
const clone = [ ...original ]
concat combines the two arrays and creates a new one.
Which One Should You Use?
Personally, I prefer the spread operator and concat over slice because my brain quickly understands what the method call does. When I see slice in my code, I need to stop for a second and remember what this method does. For me, concat is more intuitive. Choose what you like best 😃