Javascript create empty array

Create empty array with JavaScript

There are three ways you can create an empty array using JavaScript. This tutorial will help you to learn them all.

The first way is that you can get an empty array by assigning the array literal notation to a variable as follows:

The square brackets symbol [] is a symbol that starts and ends an array data type, so you can use it to assign an empty array.

The firstArr variable above will create a new empty array, while the secondArr variable will create an array with two elements.

You can also use the new Array() constructor to create a new array object like in the code below:

Both the array literal notation and the array constructor produce the same thing.

Finally, you can also create an empty array by setting the length property of your array into 0 .

The following code creates a new array with two elements, but because the length is set to 0 in the second line, the array becomes empty:

And that’s how you can create an empty array using JavaScript 😉

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How to Create an Empty Array in JavaScript

Arrays in JavaScript are one of the most useful data structures in the language.

Arrays can be used to store any number of values, and they can be used to store any type of value.

To get started with using them, you’ll want to create an empty array so that you can later on add elements to them.

In this post, we’ll learn the three easiest ways to create an empty array in JavaScript.

Using the bracket syntax

The most common way to create an empty array is to use the bracket syntax.

Let’s create an array called array using the bracket syntax:

You can confirm this is an array by using the .length property:

Another way to create an empty array is to use the Array constructor.

This more explicit way of creating an array is useful when you want to create an array with a specific length.

Let’s create an array called array using the Array constructor:

If you wanted to add values to it at the start, you can pass in the values as parameters:

Setting the length to 0

Another way to create an empty array is to set the length of an existing array to 0 .

Let’s first create an array with elements in them:

Then, we can set the length of the array to 0 :

The reason this works is because the length property is a setter as well as a getter, meaning that when you set it, it will automatically re-size the array to the new length.

Conclusion

In this post, we learned the three easiest ways to create an empty array in JavaScript.

You can either use the bracket syntax, use the Array constructor, or set the length of an existing array to 0 .

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How to Create an Empty Array in JavaScript?

Learn how to create an empty array in JavaScript and what is the concept behind it.

Table of contents

There are two ways in Javascript you can create a new empty array.

Most people use the simple declaration method to construct a new array. It’s fast and efficient.

However, if you are coming from Java or you already have an array length in mind, you can Use the constructor method to create a new array.

const myArray = new Array(arrayLength); 

How to Verify an Array?

If you want to verify if the array is created, you can use the .isArray() method.

It it’s a valid array, it should return true , else it will return false .

Can You Have an Empty Array?

Yes, you can have an empty array. If you want to check if the array is empty or not, you can use the .length property.

If the array.length returns 0, that means the array is empty.

What is The Difference Between a null Array and an Empty Array?

Technically there is nothing as a null array in javascript!

However, you can store a null value inside an array like this.

You can check if the array is empty or not by the above-mentioned method.

In JavaScript, is an empty Array Return false or true ?

 // Straight Equality [] == true; // false [] == false; // true // Conversion Boolean([]); // true ! Boolean([]); // false // Implied Conversion ! []; // false !! []; // true 

• If you check through straight equality, the empty array returns false.
• However, if you convert the empty array to a boolean assert, then the empty array returns true. It’s also the same for the forced conversion with the bang operator.

So, I recommend using .length to determine if an array is empty or not.

How to create an empty array of objects in javascript?

Creating an empty array of objects is a two-step process.

You have to use the array.push() method to add an item to the end of an empty array.

Step 1:

Create a new empty array. const sampleArr = []

Step 2:

Push an empty object inside the array. sampleArr.push(new Object())

If you want to add multiple empty objects inside an empty array, you can use a for-loop.

const n = 50; For (i = 0; i < n; i++)< sampleArr.push(new Object()) > 

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How to Declare an Empty Array in JavaScript

Here’s how to declare an empty array object in JavaScript—and what you need to do so that it meets your needs.

Suppose that, for one reason or another, you need to declare an empty array in JavaScript. (A good example of this is generating an array of letters in the English alphabet, which I recently wrote about.)

What’s the best way to do that?

There are two ways to declare an empty array object in JavaScript. One is to create a literal with brackets, and the other is to instantiate an array with the new array() constructor method.

This is how to create a literal with brackets:

And this is how to construct an array with the new Array() constructor method:

According to W3Schools, the brackets and new Array() constructor method do exactly the same. For code that’s easier for humans to read and faster for machines to interpret, use the shorter, array literal method over the longer, array constructor method.

You can then save the elements in your array object as necessary:

myArray[0] = "Apple"; myArray[1] = "Facebook"; myArray[2] = "Google"; myArray[3] = "Microsoft";

Or mutate and reassign the array object as needed (more on that, and the implementation choices you need to make to enable these two operations, below).

Declare Empty Array Only If It Doesn’t Exist

What if there’s a possibility that your array has already been declared? If you redeclare it as an empty array, you will delete all the data elements already in it—which may adversely affect your website or web application.

To only declare an empty array if that array object doesn’t already exist, use the following approach:

window.myArray = window.myArray || [];

Const, Let, or Var?

Arrays in JavaScript are objects that you can use to store multiple items under a single name. And objects, as any experienced programmer knows, can be mutated, meaning that their values can be reassigned to new arrays.

// You can mutate const arrayOne = [1, 2, 3]; const arrayTwo = [4, 5, 6]; const finalNumbers = arrayOne + "," + arrayTwo; console.log(finalNumbers); // Outputs 1,2,3,4,5,6 // But you can't reassign const currentNumbers = [1, 2, 3, 4, 5]; const currentNumbers = [6, 7, 8, 9, 10]; console.log(currentNumbers); // Outputs 1,2,3,4,5

As a matter of fact, many of JavaScript’s built-in methods for array objects enable you to mutate those objects economically, with vanilla code. However, not all arrays can be reassigned.

// You can mutate let arrayOne = [1, 2, 3]; let arrayTwo = [4, 5, 6]; let finalNumbers = arrayOne + "," + arrayTwo; console.log(finalNumbers); // Outputs 1,2,3,4,5,6 // And you can reassign let currentNumbers = [1, 2, 3, 4, 5]; let currentNumbers = [6, 7, 8, 9, 10]; console.log(currentNumbers); // Outputs 6,7,8,9,10

Whether to declare your array as a constant or variable comes down to what you can—and cannot—do with it as a result:

• If you declare your array as a const , you can mutate the array object but you can’t reassign it;
• If you declare your array as a let or var , you can mutate the array object and reassign it. The choice between let and var is as follows:
  • Declaring the array as var scopes it globally or to the function body;
  • Declaring the array as let scopes it to the statement between curly brackets (<>).

  This has significant implications for your code and logic. For example, if you need to empty an array every now and then, declaring it as a constant will not work for you; declaring it as a variable is the way to go.

  To put these trade-offs in a table:

  Declaration	Scope	Mutable	Reassinable
  Const	Global (or function)	Yes	No
  Let	Global (or function)	Yes	Yes
  Var	Statement	Yes	Yes

  Feel free to bookmark this post and reference it as needed.

  In Conclusion

  It’s easy to declare an empty array in JavaScript. What’s hard is choosing exactly how to do it, so that you can manipulate the array object as you need in your app.

  With the knowledge bomb I dropped on you all above, I hope that choice is less hard to make. Thanks for reading this far, and be sure to add anything I may have missed or that’s worth including in the comments below.

  Leave a comment Cancel reply

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