Javascript Array keys which holds sub-arrays

Question

I have an array which holds sub-arrays, the main array has custom keys; used as an identifier. The problem is I can't access the array with these keys set e.g:

array.length - returns 0 when clearly it has values

In console:

[evt1: Array[0], evt2: Array[0]]
evt1: Array[0]
evt2: Array[0]

When changed back to a standard index (0,1,2), the array can be accessed - and performs as normal. Why is this happening?

Thanks

Arrays dont have keys, they have indexes. Objects have keys, and each key of an object could contain an array. — tymeJV
– tymeJV, Commented Apr 23, 2014 at 20:11
@tymeJV To be picky, the arrays are objects and they get a key/property for each index e.g. [4,5,6].hasOwnProperty('1') //true — Johan
– Johan, Commented Apr 23, 2014 at 20:17

juvian · Accepted Answer · 2014-04-23 20:13:11Z

1

As stated in comments, you are not using an array, you are using an object. Use Object.keys(your_object).length to get length, and to travel through indexes:

for(var index in your_object){
    console.log(index,your_object[index]);
}

You can also do:

var indexes=Object.keys(your_object);
for(var i=0;i<indexes.length;i++){
    console.log(indexes[i], your_object[indexes[i]]);
}

answered Apr 23, 2014 at 20:13

juvian

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4 Comments

Johan Over a year ago

@Martin The for..in loop is used to iterate object properties in Javascript

xyhhx Over a year ago

I know that. But I've never seen this way of iterating over objects

Johan Over a year ago

@Martin Then what have you seen o.O

xyhhx Over a year ago

Ok I've seen the for ... in loops before (obviously) but I've never seen Object.keys(your_object).length to be used in a regular for loop. The answer was edited since my first comment

user400654 · Accepted Answer · 2014-04-23 20:15:14Z

1

Arrays (like many other things in javascript) can have properties just like objects, however, array properties do not count toward the length of the array. What you should use is an object as the outer structure that contains your keys->arrays.

{evt1: Array[0], evt2: Array[0]}

answered Apr 23, 2014 at 20:15

user400654

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