Idiomatically accessing json objects with clojurescript

Question

Anyone have any docs for idiomatic clojurescript for access a javascript object (returned as json, essentially a hash)?

I have a JSON object returned via an AJAX request:

{
  list: [1,2,3,4,5],
  blah: "vtha",
  o: { answer: 42 }
}

How do I access these fields using clojurescript?

I can do:

(.-list data)

But how does this work when I have nested values and objects?

(.-answer (.-o data))

The above seems to be quite clumsy, especially given the nice js syntax of: data.o.answer.

What is the idiomatic way of accessing json objects with clojurescript?

Note:

I realised that I can actually refer to elements using JS syntax, which is quite handy actually. So the following will work correctly:

(str data.o.answer)

So far I think the answer is really: there is no idiomatic way of doing this (yet). — Toby Hede, Mar 24 '12 at 23:07
Last response was a while ago -- is (str data.o.answer) idiomatic? — cnp, Dec 27 '15 at 06:50

score 17 · Answer 1 · edited Apr 28 '13 at 09:17

17

You probably want aget:

(aget foo "list")

~~aget isn't variadic yet, but hopefully will be soon~~ it's variadic now. (aget data "o" "answer") would work

edited Apr 28 '13 at 09:17

om-nom-nom

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answered Mar 22 '12 at 16:26

dnolen

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For the record, it's variadic now. (aget data "o" "answer") would work. – Kris Jenkins Feb 28 '13 at 15:20
FWIW, David would retract this answer these days, and suggest instead `(goog.object/get foo "list")`. See more in the answer by Jiacai Liu. – Mike Fikes Jan 29 '18 at 14:22

sw1nn · Answer 2 · 2014-04-14T20:50:31.387

11

Firstly, your proposed syntax for nested access does work:

ClojureScript:cljs.user> (def data 
    (JSON/parse "{\"list\": \"[1,2,3,4,5]\", \"blah\": \"vtha\", \"o\": {\"answer\": \"42\"}}"))
#<[object Object]>
ClojureScript:cljs.user> (.-answer (.-o data))
"42"

You can use the threading macros...

ClojureScript:cljs.user> (-> data (.-o) (.-answer))
"42"

Or .. notation

ClojureScript:cljs.user> (.. data -o -answer)
"42"

edited Apr 14 '14 at 20:50

answered Mar 22 '12 at 11:07

sw1nn

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Does indeed work, still seems clunky to me, even with threading macros. – Toby Hede Mar 24 '12 at 23:08
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the parens in the threading are redundant `(-> data .-o .-answer)` – noisesmith Apr 14 '14 at 16:00
1

@noisesmith these days I'd prefer to use ``(.. data -o -answer)``, as noted by @stephen-nelson - i'll update the answer – sw1nn Apr 14 '14 at 20:47

score 6 · Answer 3 · answered Mar 22 '12 at 14:39

6

If you're dealing with any amount of data, I'd convert the JSON into clojure data structures and then use the usual idioms:

(let [my-json (js* "{
                     list: [1,2,3,4,5],
                     blah: \"vtha\",
                     o: { answer: 42 }
                   }")
      converted (js->clj my-json)]

  (get-in converted ["list" 3]) ;; => 4
  (-> converted "o" "answer") ;;=> 42
)

(Note: don't use js* if you can help it; it's not idiomatic and might go away in future versions of ClojureScript.)

answered Mar 22 '12 at 14:39

Kevin L.

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I'm finding that the data is converted into a vector rather than a hash, so actually more co,plicated to extract data from than the default js object – Toby Hede Mar 24 '12 at 23:03
Actually, the converted data seems to vary unpredictably ... obj map or vector – Toby Hede Mar 24 '12 at 23:04
This is like buying the whole grocery store just to get the oranges. A waste of resources. – Nikita Volkov Oct 09 '15 at 01:10

score 2 · Answer 4 · answered Apr 26 '13 at 23:53

Clojurescript has a .. operator that is useful for chained javascript calls:

(.. data -o -answer) => data.o.answer => 42
(aget (.. data -list) 1) => data.list[1] => 2

You can use most list operators on arrays too, e.g.

(into [] (.. data -list)) ; vector [1 2 3 4]

score 2 · Answer 5 · answered Jan 29 '18 at 13:34

2

Forget about aget, it's mainly designed for array (array get). Use

goog.object/get
goog.object/set

https://clojurescript.org/news/2017-07-14-checked-array-access

answered Jan 29 '18 at 13:34

Jiacai Liu

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Idiomatically accessing json objects with clojurescript

5 Answers5