length is a property available on arrays (and strings), size is a property available on Set objects (i.e. those created with new Set()).
If you follow along in the video or workspaces and then log out the length of the set to the console, you'll see it doesn't give you the same value as the size, because it doesn't exist.
js
console.log('classroom.length:', classroom.length);
// undefined Answer from Iain Simmons on teamtreehouse.com
SitePoint
sitepoint.com › blog › javascript › do i use .size() or .length in javascript?
Do I use .size() or .length in Javascript? — SitePoint
February 12, 2024 - However, they are used with different types of objects. The length property is used with array objects, while the size property is used with Map and Set objects. The length property of an array returns the number of elements in the array. On the other hand, the size property of a Map or Set ...
Top answer 1 of 2
1
length is a property available on arrays (and strings), size is a property available on Set objects (i.e. those created with new Set()).
If you follow along in the video or workspaces and then log out the length of the set to the console, you'll see it doesn't give you the same value as the size, because it doesn't exist.
js
console.log('classroom.length:', classroom.length);
// undefined
2 of 2
0
Hello Stavros!
Length will give you the numbers of items in an array. For example:
Return the length of an array:
js
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.length;
*** The result will be: 4 ***
Size... in the following code if you click the button, you will also get a return of 4, because JavaScript makes the browser only select 4 from the list of 7.
```html
Cat
Dog
Horse
Elephant
Mouse
Fish
Cow
Click the button to change the number of visible options in the dropdown list.
Try it ```htmljavascript - Array.size() vs Array.length - Stack Overflow
What is the difference between the two? So I know that array.size() is a function while array.length is a property. Is there a usecase for using one over the other? Is one more efficient? (I would More on stackoverflow.com
jQuery size() method vs length attribute - Stack Overflow
Bring the best of human thought and AI automation together at your work. Explore Stack Internal ... Save this question. Show activity on this post. Is there any difference between $(".selector").size() and $(".selector").length ? More on stackoverflow.com
Difference between .length() and .length?
The .length of a String is a property, not a function, as per ECMAScript spec . More on reddit.com
3
15
March 5, 2016Differentiate between length and length()
Differentiate between length and length() · Differentiate between Linear search and Binary search More on knowledgeboat.com
1
138
February 16, 2021findnerd
findnerd.com › list › view › Difference-between-size-and-length-in-Javascript › 21751
Difference between size() and length in Javascript
June 30, 2016 - 1. length is a property which works faster as compared to size() function, the reason behind this is that the length is a property and size is a function and we know that any property works faster than any function or method.
C# Corner
c-sharpcorner.com › home › interviews › jquery › what is the difference between size and length of jquery?
What is the difference between size and length of jQuery?
Size() and length in jQuery both returns the number of element in an object but length is faster than the size because length is a property and size is a method and length property does not have the overhead of a function call.
TutorialsPoint
tutorialspoint.com › article › What-is-the-difference-between-jQuery-size-and-jQuery-length
What is the difference between jQuery.size() and jQuery.length?
<!DOCTYPE html> <html> <head> <script ... jQuery.size() and jQuery.length return the count of elements, but length is preferred as it's a property rather than a method, making it faster and compatible with modern jQuery versi...
Linux Hint
linuxhint.com › array-size-vs-array-length-javascript
Linux Hint – Linux Hint
Linux Hint LLC, [email protected] 1210 Kelly Park Circle, Morgan Hill, CA 95037 Privacy Policy and Terms of Use
Top answer 1 of 10
632
Array.size() is not a valid method
Always use the length property
There is a library or script adding the size method to the array prototype since this is not a native array method. This is commonly done to add support for a custom getter. An example of using this would be when you want to get the size in memory of an array (which is the only thing I can think of that would be useful for this name).
Underscore.js unfortunately defines a size method which actually returns the length of an object or array. Since unfortunately the length property of a function is defined as the number of named arguments the function declares they had to use an alternative and size was chosen (count would have been a better choice).
2 of 10
191
.size() is not a native JS function of Array (at least not in any browser that I know of).
.length should be used.
If
.size() does work on your page, make sure you do not have any extra libraries included like prototype that is mucking with the Array prototype.
or
There might be some plugin on your browser that is mucking with the Array prototype.
GeeksforGeeks
geeksforgeeks.org › javascript › what-is-the-difference-between-array-size-and-array-length-in-javascript
Difference between array.size() and array.length in JavaScript - GeeksforGeeks
July 12, 2025 - Here in JavaScript array.size() is invalid method so array.length property should be used. Below examples implement the above concept: Example 1: This example demonstrates array.size() method and array.length property. ... <!DOCTYPE html> <html> <head> <title> Difference between array.size() method and array.length property </title> </head> <body> <p> Click the button to display the length of array.
CodingTechRoom
codingtechroom.com › question › when-to-use-length-vs-length
Understanding When to Use .length vs .length() in Programming - CodingTechRoom
What is the difference between .length and .length() in programming? Copied · // Example in JavaScript let arr = [1, 2, 3]; console.log(arr.length); // Output: 3 // Example in Java String str = "Hello"; int length = str.length(); // Output: 5 · In programming, both .length and .length() are used to determine the size or length of various data structures, but they apply to different contexts and languages.
Medium
medium.com › @amirakhaled2027 › string-length-vs-string-size-in-javascript-393ec8d77a3b
string.length vs string.size in JavaScript | by Amira Khaled | Medium
August 24, 2024 - This article will provide you with a clear explanation on the difference between them. The string.length property returns the number of characters in a string, including spaces, punctuation marks, and special characters.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › String › length
String: length - JavaScript - MDN Web Docs - Mozilla
3 weeks ago - The actual space used by a string is subject to JavaScript engine optimizations, and all major engines use a more compact internal representation, such as one-byte storage, for strings containing only Latin-1 characters. If you are working with large strings in other encodings (such as UTF-8 files or blobs), note that when you load the data into a JS string, the encoding always becomes UTF-16. The size of the string may be different from the size of the source file.
Reddit
reddit.com › r/learnjavascript › difference between .length() and .length?
r/learnjavascript on Reddit: Difference between .length() and .length?
March 5, 2016 -
I was practicing and came across something strange... when I wanted to find the character length of html inside a div I used
$('.count').text(function(){ return $('.words').text().length; });
which gave me a number (8 in this case) whereas using .length() didn't show anything. What is .length? I thought all methods had to have a () at the end? What is this black magic?
Top answer 1 of 3
9
The .length of a String is a property, not a function, as per ECMAScript spec .
2 of 3
8
.length() is something you'll come across a lot while using jQuery as it's a common jQuery method. However, as soon as you call .text() you're being given a regular String object; you've now stepped outside of your library and into vanilla JS. The same goes with checking the lengthproperty of an Array. When you check $(".words").length() you're checking how many jQuery objects exist within that jQuery collection.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › Array › length
Array: length - JavaScript - MDN Web Docs
It’s been available across browsers since July 2015. ... The length data property of an Array instance represents the number of slots in that array. The value is an unsigned, 32-bit integer that is always numerically greater than the highest index in the array.
Sololearn
sololearn.com › en › Discuss › 1464005 › size-and-length-in-javascript
size and length in javascript | Sololearn: Learn to code for FREE!
what is the difference between ... that you think about about: array.size() and array.length array.length is property that returns number of elements in array....
W3Schools
w3schools.com › jsref › jsref_length_array.asp
JavaScript Array length Property
The length property sets or returns the number of elements in an array.
SheCodes
shecodes.io › athena › 24496-what-is-length-in-javascript
[JavaScript] - What is .length in JavaScript? - SheCodes | SheCodes
Explanation of the .length property in JavaScript for arrays and strings.
GeeksforGeeks
geeksforgeeks.org › jquery › difference-between-jquery-size-and-jquery-length
Difference between jquery.size() and jquery.length - GeeksforGeeks
July 23, 2025 - Here, We can clearly see that size() method is internally calling the length property.
Codecademy
codecademy.com › forum_questions › 5286bae4548c35db2400242d
Why store the length of the array in a variable instead of using .length? | Codecademy
The .length variable is internally calculated whenever the size of the array changes and therefore no additional/wasted calculations are performed and the .length variable is always representative of the current state of the array.