How to get JavaScript hash table count?

Question

Possible Duplicate:
Length of Javascript Associative Array

hash_table = {a: 131, b: 222, c:313}

The length method is not working of course since it will be confused with a key.

So how do I do it?

From the duplicate question, a useful answer that's not here. Use underscore's size, _.size(). http://stackoverflow.com/a/11346637/1684480 — Thaddeus Albers, Sep 07 '13 at 06:19

score 83 · Accepted Answer · answered Jan 02 '12 at 14:55

83

Object.keys will return all the keys in the object as a list, then use length to get the length.

example:

Object.keys(hash_table).length

NOTE that this is ECMA 5 and may not be available in some browsers. see https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/keys for full document.

answered Jan 02 '12 at 14:55

qiao

Would it return also inherited properties ? – rsk82 Jan 02 '12 at 14:57
Nope, it will return only own properties. – qiao Jan 02 '12 at 14:59
As I understand it, Object.keys is not supported in IE8 and lower, so beware... – Irongaze.com Aug 09 '12 at 17:38
1

Always supported in 2017 :) – Plaute May 23 '17 at 14:34

simonecampora · Answer 2 · 2012-01-02T16:36:55.060

1

var count = 0;
for ( property in hash_table ) count++;

edited Jan 02 '12 at 16:36

answered Jan 02 '12 at 15:11

simonecampora

JSON is a data exchange format and has nothing to do with JavaScript, besides the name and similar syntax. JavaScript does not have "Associative Arrays", only arrays. – Felix Kling Jan 02 '12 at 15:14
thanks for your feedbacK: I have edited my answer accordingly! – simonecampora Jan 02 '12 at 15:18
Still, what do you mean by "using Arrays in associative fashion"? The `length` property is only updated for numerical properties,i.e. `arr[0] = 42.`. Non-numerical properties do not update `length` and should not be used for arrays as it is just confusing. – Felix Kling Jan 02 '12 at 16:04
please find more detailes here: http://en.wikipedia.org/wiki/JavaScript_syntax#Array "One can use the object declaration literal to create objects that behave much like associative arrays" but indeed I was wrong. I will edit my answer – simonecampora Jan 02 '12 at 16:34

2 Answers2