CODEWITHSUNDEEP
javascriptarrays
Abraham P
Abraham P

Reputation: 15471

Array.size() vs Array.length

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 imagine .length to be significantly faster as it is a property rather then a method call?) Why would one ever use the slower option? Are there some browsers that are incompatible with one or the other?

var x = [];
console.log(x.size());
console.log(x.length);
console.log(x.size()==x.length);
x =[1,2,3];
console.log(x.size());
console.log(x.length);
console.log(x.size()==x.length);

Will print:

0, 0, true
3, 3, true

Upvotes: 475

Views: 982737

Answers (10)

Saurabh Chandra Patel
Saurabh Chandra Patel

Reputation: 13596

The .size() function is available in Jquery and many other libraries.

The .length property works only when the index is an integer.

The length property will work with this type of array:

var nums = new Array();
nums[0] = 1; 
nums[1] = 2;
print(nums.length); // displays 2

The length property won't work in the following case:

var pbook = new Array(); 
pbook["David"] = 1; 
pbook["Jennifer"] = 2;
print(pbook.length); // displays 0

The reason is that JavaScript does not support indexes of type string in arrays but objects (as properties), and pbook or an object of prototype Array named "pbook" would now have two properties assigned ("David" and "Jennifer"; i.e. pbook.David) and represent an empty array.

const a = []; // Relatively the same as: const a = new Array();

a['0a'] = 123; a['2'] = 456; a[1] = 789;

console.log(`a(${a.length}) = `, a);
console.log(`Enumerable properties of ${Object.prototype.toString.call(a)} = `, Object.keys(a));

So in your case you should be using the .length property.

For objects, please consider the following:
- Length of a JavaScript object;
- Object.getOwnPropertyNames vs Object.keys.

Upvotes: 40

cskwg
cskwg

Reputation: 849

The property 'length' returns the (last_key + 1) for arrays with numeric keys:

var  nums  =  new  Array();
nums [ 10 ]  =  10 ; 
nums [ 11 ]  =  11 ;
log.info( nums.length );

will print 12!

This will work:

var  nums  =  new  Array();
nums [ 10 ]  =  10 ; 
nums [ 11 ]  =  11 ;
nums [ 12 ]  =  12 ;
log.info( nums.length + '  /  '+ Object.keys(nums).length );

Upvotes: 11

Sunali Bandara
Sunali Bandara

Reputation: 410

we can you use .length property to set or returns number of elements in an array. return value is a number

> set the length: let count = myArray.length;
> return lengthof an array : myArray.length

we can you .size in case we need to filter duplicate values and get the count of elements in a set.

const set = new set([1,1,2,1]); 
 console.log(set.size) ;`

Upvotes: 1

AmerllicA
AmerllicA

Reputation: 32502

Actually, .size() is not pure JavaScript method, there is a accessor property .size of Set object that is a little looks like .size() but it is not a function method, just as I said, it is an accessor property of a Set object to show the unique number of (unique) elements in a Set object.

The size accessor property returns the number of (unique) elements in a Set object.

const set1 = new Set();
const object1 = new Object();

set1.add(42);
set1.add('forty two');
set1.add('forty two');
set1.add(object1);

console.log(set1.size);
// expected output: 3

And length is a property of an iterable object(array) that returns the number of elements in that array. The value is an unsigned, 32-bit integer that is always numerically greater than the highest index in the array.

const clothing = ['shoes', 'shirts', 'socks', 'sweaters'];

console.log(clothing.length);
// expected output: 4

Upvotes: 1

rev
rev

Reputation: 27

Size detects duplicates, it will return the number of unique values

const set1 = new Set([1, 2, 3, 4, 5, 5, 5, 6]);
console.log(set1.size);
// expected output: 6

Upvotes: 1

Davy
Davy

Reputation: 1786

The .size() method is deprecated as of jQuery 1.8. Use the .length property instead

See: https://api.jquery.com/size/

Upvotes: 4

user2811108
user2811108

Reputation: 191

array.length isn't necessarily the number of items in the array:

var a = ['car1', 'car2', 'car3'];
a[100] = 'car100';
a.length; // 101

The length of the array is one more than the highest index.

As stated before Array.size() is not a valid method.

More information

Upvotes: 19

Julio Flores
Julio Flores

Reputation: 433

.size() is jQuery's, much probably you're either confusing with or took from someone else who had imported the jQuery library to his project.

If you'd have jQuery imported and you'd write like $(array).size(), it would return the array length.

Upvotes: 21

Gabriel
Gabriel

Reputation: 18780

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).

Upvotes: 628

Naftali
Naftali

Reputation: 146302

.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.

Upvotes: 190

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