An Empty Set Produced a Size of 5

Question

An Empty Set Produced a Size of 5

Recently, I began delving into the Rapid JavaScript Training course by Mark Zamoyta on PluralSight and encountered a fascinating concept. Through two examples, he demonstrated an intriguing concept that I've been attempting to comprehend.

I'm puzzled about how the length of entries is captured after creating an array using the new Array() method, especially since it resulted in an empty array []. In theory, shouldn't it return -1 since it's empty like this []?

  var entries = [1,2,3,4,5];
  entries.length
  => 5
  entries
  => [ 1, 2, 3, 4, 5 ]

  var entries = new Array(5);
  entries.length
  => 5
  entries
  => []

javascript arrays reference-type

Answer 1

Answer №1

let myArray = new Array(5);

If you create an array by specifying the size in the constructor as shown above, memory space will be reserved for 5 elements in the array. Upon inspection, the array would look like this:

console.log(myArray[1]);
=> undefined
console.log(myArray.toString);
=> ,,,,

It's evident that the array has five slots, each containing the value of undefined. Therefore, the array isn't truly empty.

Initialising an array in this manner may not be considered best practice, as there is limited utility in doing so. If you attempt to add elements using push, the result will be as follows:

myArray.push("value");
console.log(myArray.toString);
=> ,,,,,value

This outcome is likely not desired. It is recommended to initialise arrays without specifying a size to avoid such situations:

let myArray = [];

Answer 2

let myArray = new Array(5);

If you create an array by specifying the size in the constructor as shown above, memory space will be reserved for 5 elements in the array. Upon inspection, the array would look like this:

console.log(myArray[1]);
=> undefined
console.log(myArray.toString);
=> ,,,,

It's evident that the array has five slots, each containing the value of undefined. Therefore, the array isn't truly empty.

Initialising an array in this manner may not be considered best practice, as there is limited utility in doing so. If you attempt to add elements using push, the result will be as follows:

myArray.push("value");
console.log(myArray.toString);
=> ,,,,,value

This outcome is likely not desired. It is recommended to initialise arrays without specifying a size to avoid such situations:

let myArray = [];

Answer 3

Answer №2

The size of an array in JavaScript is not dynamically calculated using the length property. Instead, it can be manually set through the constructor or by an assignment, and it adjusts as elements are added or removed (Reference):

Whenever a property with an array index as its name is added, the length property is updated to be one more than the numeric value of that index if necessary.

This property is constantly updated and not calculated. For example, using the constructor new Array(5) will initialize an array with a length of 5. You can also manually set the length, which will either fill in with undefined or truncate the array accordingly:

var myArray = [];
myArray.length = 3;
// myArray is now [undefined, undefined, undefined]

Answer 4

The size of an array in JavaScript is not dynamically calculated using the length property. Instead, it can be manually set through the constructor or by an assignment, and it adjusts as elements are added or removed (Reference):

Whenever a property with an array index as its name is added, the length property is updated to be one more than the numeric value of that index if necessary.

This property is constantly updated and not calculated. For example, using the constructor new Array(5) will initialize an array with a length of 5. You can also manually set the length, which will either fill in with undefined or truncate the array accordingly:

var myArray = [];
myArray.length = 3;
// myArray is now [undefined, undefined, undefined]

An Empty Set Produced a Size of 5

Answer №1

Answer №2

Similar questions

Changing the CSS class of the Bootstrap datetime picker when selecting the year

Error encountered while parsing JSON data from LocalStorage

SyntaxError: An invalid character was encountered (at file env.js, line 1, column 1)

Code not functioning properly in Internet Explorer

What is the necessity of explicitly requesting certain core modules in Node.js?

Generate an image of a "button" with dynamic hover text

Is it recommended to place the styles created by material-ui for child components after the styles generated for the parent component?

Guide to retrieving PDFs and images from a Spring Application as an API response and manipulating the data using JS/React

Utilize Javascript to pull information from a REST API and generate a dynamic table with the retrieved

What is the proper way to utilize JQuery and Ajax to communicate with a global function in writing?

Integrate an input field with a copy function similar to the GitHub clone view

What is the best way to effectively clear memory in THREE.js?

Clear Vuex state upon page refresh

Unravel a Base64 encoded string with the power of CryptoJS

Matching exact multiple words with special characters using Javascript Regular Expression

Aligning validation schema with file type for synchronization

JQuery is having trouble with playing multiple sound files or causing delays with events

Experiencing issues with applying bootstrap style to pagination when using react-js-pagination

Error: Identifier Not Expected (Exploring Generators in ES6)

Using jQuery to save PHP form output into an Excel spreadsheet