Getting keys from associative array in javascript

Question

In javascript (or CoffeScript) is there a way to just get the keys for a associative array? The real problem I am trying to solve is to create a set but the only way I found that is to create a map and use the keys to produce the set. I know I can iterate over the elements and collect them but that seems like extra work to me.

So for example in CoffeeScript I could do:

foobar = { "a": true, "b": true, "c": true }
keys = []
keys.push k for k,v of foobar

Which honestly isn't that much code but is there really no other way to do a set or just get the keys from an associative array without writing a special class or pulling in a separate library?

UPDATE: I have a requirement that IE < 9 needs to be supported so unfortunately Object.keys(foobar) is out. Good suggestion though, sorry I missed this req in the original question.

developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… There is a IE6+ polyfill too. — Derek 朕會功夫
– Derek 朕會功夫, Commented Jan 22, 2014 at 4:12
Sorry I should have mentioned that i'd seen Object.keys before. Unfortunately IE < 9 is a requirement. — ajorgensen
– ajorgensen, Commented Jan 22, 2014 at 4:23
You may want to see this code for mimicking some set-like functionality in javascript: stackoverflow.com/questions/7958292/… — jfriend00
– jfriend00, Commented Jan 22, 2014 at 4:27

Bergi · Accepted Answer · 2014-01-23 13:59:33Z

4

If you don't want to use Object.keys or Object.getOwnPropertyNames (or their respective shims), coffeescript offers very nice loop comprehensions:

keys = (k for own k of foobar) // == Object.keys foobar
keys = (k for k of foobar)

edited Jan 23, 2014 at 13:59

answered Jan 22, 2014 at 4:27

Bergi

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jfriend00 · Accepted Answer · 2014-01-22 04:28:50Z

1

You can use Object.keys() and the polyfill here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys for browsers that don't support that.

answered Jan 22, 2014 at 4:28

jfriend00

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