Skip to main content

What are three dots (…) in Javascript - React Native & React

What are three dots (…) in Javascript

The spread syntax is a new addition to the set of operators in JavaScript ES6. It takes in an iterable (e.g an array) and expands it into individual elements.

The spread syntax is commonly used to make shallow copies of JS objects. Using this operator makes the code concise and enhances its readability.

Syntax

The spread syntax is denoted by three dots, ….

let array = [...value]

Examples

Since the array data structure is widely used, it will be considered in all the subsequent examples.

1. Copying an array

The array2 has the elements of array1 copied into it. Any changes made to array1 will not be reflected in array2 and vice versa.

If the simple assignment operator had been used then array2 would have been assigned a reference to array1 and the changes made in one array would reflect in the other array which in most cases is undesirable.

let array1 = ['h', 'e', 'l', 'l', 'o'];
let array2 = [...array1];
console.log(array2);['h', 'e', 'l', 'l', 'o'] // output

2. Inserting the elements of one array into another

It can be seen that the spread syntax can be used to append one array after any element of the second array. In other words, there is no limitation that desserts can only be appended at the beginning of the end of the desserts1 array.

let desserts = ['cake', 'cookie', 'donut'];
let desserts1 = ['icecream', 'flan', 'frozen yoghurt', ...desserts];
console.log(desserts);//Appending baked_desserts after flan
let desserts2 = ['icecream', 'flan', ...desserts, 'frozen yoghurt'];
console.log(desserts2);// output
[ 'cake', 'cookie', 'donut' ]
[ 'icecream', 'flan', 'cake', 'cookie', 'donut', 'frozen yoghurt' ]

3. Array to arguments

function multiply(number1, number2, number3) {
  console.log(number1 * number2 * number3);
}
let numbers = [1,2,3];
multiply(...numbers);

Instead of having to pass each element like numbers[0], numbers[1] and so on, the spread syntax allows array elements to be passed in as individual arguments.

//Passing elements of the array as arguments to the Math Object
let numbers = [1,2,300,-1,0,-100];
console.log(Math.min(...numbers));

The Math the object of Javascript does not take in a single array as an argument but with the spread syntax, the array is expanded into a number of arguments with just one line of code.

I hope you enjoyed this post.

Show some Love in Comments...

Comments

Post a Comment

Thank You.

Popular Posts

16 AWS Gotchas

16 AWS Gotchas In January I launched the MVP for my own startup,  Proximistyle , which helps you find what you’re looking for nearby. On advice from friends and industry contacts I chose AWS as my cloud provider. Having never had to set up my own cloud infrastructure before, the learning curve to get from no experience to a stable VPC system I was happy with was significantly steeper than expected, and had its fair share of surprises. #1 Take advantage of the free resources offered AWS offers a free tier for new accounts. If you have recently bought a domain and set up a company you qualify for the free tier for a year. Additionally, if you are a bootstrapped startup you can apply for  the Startup Builders package  and get $1000 in AWS credits. After doing the above, you’re now ready to get started with setting up the AWS infrastructure for your startup. #2 Set up billing budgets and alerting The very first thing you should do after setting up billing, is enabling a budge...
Post a Comment
Read more

Ultimate Folder Structure For Your React Native Project

  Ultimate Folder Structure For Your React Native Project React native project structure React Native is a flexible framework, giving developers the freedom to choose their code structure. However, this can be a double-edged sword for beginners. Though it offers ease of coding, it can soon become challenging to manage as your project expands. Thus, a structured folder system can be beneficial in many ways like better organization, simplified module management, adhering to coding practices, and giving a professional touch to your project. This write-up discusses a version of a folder arrangement that I employ in my React Native projects. This structure is based on best practices and can be modified to suit the specific needs of your project. Before we get into the project structure let’s give credit to @sanjay who has the original idea of the structure but I modify his version of the code, to make it better. Base library axios  — For network calling. react-navigation ...
Post a Comment
Read more

Master Map & Filter, Javascript’s Most Powerful Array Functions

Master Map & Filter, Javascript’s Most Powerful Array Functions Learn how Array.map and Array.filter work by writing them yourself This article is for those who have written a  for  loop before, but don’t quite understand how  Array.map  or  Array.filter  work. You should also be able to write a basic function. By the end of this, you’ll have a complete understanding of both functions, because you’ll have seen how they’re written. Array.map Array.map  is meant to transform one array into another by performing some operation on each of its values. The original array is left untouched and the function returns a new, transformed array. For example, say we have an array of numbers and we want to  multiply each number by three . We also don’t want to change the original array. To do this without  Array.map , we can use a standard for-loop. for-loop var originalArr = [1, 2, 3, 4, 5]; var newArr = []; for(var i = 0; i < originalArr.length; i+...
Post a Comment
Read more