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This question already has an answer here:

I'm having a hard time understanding this code. Could someone try to explain why an array can have elements and 0 length?

var myArray = [];
myArray["hello"] = 4;
myArray["world"] = 65;
$('#btn').on('click',function() {
    console.log(myArray.length); // Prints 0
    console.log(myArray); // Prints [hello: 4, world: 65]
    console.log(myArray.length); // Prints 0
 }
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marked as duplicate by Pointy Jul 25 '14 at 16:11

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
    
this is not asynchronous, and you're using a framework hidding to you 80% of the fun of javascript. So, please don't forget it in your tags (I added it for you) –  Sebas Jul 25 '14 at 16:10
    
you might want Object.keys(myArray).length, but you should likely use an object instead of an array. –  dandavis Jul 25 '14 at 16:11
    
Length only adds numerically indexed properties, you're using the Array in this example as a dictionary. If you want to loop through the Array, you could put the String and Number into an Object and insert that into the Array. –  Evin Ugur Jul 25 '14 at 16:14

1 Answer 1

up vote 4 down vote

The .length property only pertains to numerically-indexed properties.

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2  
No offense, @Pointy but, although true, this isn't really the answer to the question. What he's done here is instantiate a new array object, then add properties to that object named hello and world. He's setting properties of the array object, not elements of the array itself. –  Grinn Jul 25 '14 at 16:15
1  
@grinn: FWIW, array elements are so properties of the object. Every property with a numerical, positive 32bit ( or so) property name is considered to be an element . –  Felix Kling Jul 25 '14 at 16:31
    
This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. –  acrosman Jul 25 '14 at 16:59
    
@acrosman the question is a duplicate; there's a fine explanation in the linked question. –  Pointy Jul 25 '14 at 17:10
    
@Grinn yes, as Felix Kling notes there really are no semantic differences between numerically-indexed properties and string-indexed properties; indeed, the numerically-indexed properties are really strings too! The .length property reflects an internal interpretation of the named properties, and those semantics are based on the properties whose names look like non-negative integers. –  Pointy Jul 25 '14 at 17:12

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