Get JSON property from fully qualified string

Question

Say I have a JSON object like this:

var a = {
  "b" : {
    "c" : 1
  }
}

is there a quick way to get at c when I know the string "b.c" ?

I guess I could split the string by dots then drill down into c from that but I was hoping there was a quick way to do this in one go.

like I was hoping maybe var c = a["b.c"] but that doesnt work

@JanDvorak Look at the link I give, it links to many answers for getting a deep property from a path. — Denys Séguret, Feb 15 '13 at 16:09
For example it links to this question : http://stackoverflow.com/questions/10934664/convert-string-in-dot-notation-to-get-the-object-reference — Denys Séguret, Feb 15 '13 at 16:11
@dystroy: this question is not a duplicate of #14396647. It may require an answer that mentions `eval`, but it's absolutely not the same question. — Paul D. Waite, Feb 15 '13 at 16:11
@PaulD.Waite I preferred the first link I gave because Bergi made an answer linking to 6 or 7 duplicates of this daily question. — Denys Séguret, Feb 15 '13 at 16:14

musefan · Accepted Answer · 2013-02-15T16:44:48.287

4

How about something like this, as you suggested using a split:

var a = {
  "b" : {
    "c" : 1
  }
}

var n = "b.c".split(".");
var x = a;
for(var i = 0; i < n.length; i++){
   x = x[n[i]];
}
//x should now equal a.b.c

Here is a working example

In the event that the path is not valid, there is some extra checking that should be done. As my code stands above, x will be undefined if the final part of the path is invalid (e.g "b.d"). If any other part of the path is invalid (e.g. "d.c") then the javascript will error.

Here is a modified example that will end the loop at the first instance of undefined, this will leave x as undefined and will ensure the javascript can continue to execute (no error!)...

var n = "d.c".split(".");
var x = a;
for (var i = 0; i < n.length; i++) {
    x = x[n[i]];
    if (typeof(x) == "undefined") {
        break;
    }
}

Here is an example of this in action

edited Feb 15 '13 at 16:44

answered Feb 15 '13 at 16:12

musefan

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+1; doesn't require ES5 – John Dvorak Feb 15 '13 at 16:16
1

Note that it would be nice if you returned `undefined` if any part of the key is missing – John Dvorak Feb 15 '13 at 16:17
@JanDvorak: It actually does return undefined, try changing "b.c" to "b.d". Although I appreciate it does not break the loop early at the first `undefined` that it finds. Ill have a play and edit ;-) – musefan Feb 15 '13 at 16:19
@JanDvorak: Not with my edit it doesn't. Keep up! – musefan Feb 15 '13 at 16:26
Nice change. However, what about `a={zero:0}; n="zero.toString"`? :-) It _should_ return a function, but doesn't – John Dvorak Feb 15 '13 at 16:28
@JanDvorak: How about now? better? I could also evaluate the function so that "zero.toString.length" returns `0` – musefan Feb 15 '13 at 16:46
I like it, better now :-) – John Dvorak Feb 15 '13 at 16:49
I wouldn't recommend functions you encounter, but you can access their properties (as you already do) – John Dvorak Feb 15 '13 at 16:50

score 1 · Answer 2 · answered Feb 15 '13 at 16:12

var a = {
  "b" : {
    "c" : 1
  }
}

var c = "b.c".split(".").reduce(function(obj, key) {
    return obj[key];
}, a);

alert(c)

See reduce. The link also show a how to implement shim for the browsers that doesn't support ES5. Notice that this code is simplified, assumes the keys are present in the objects.

Get JSON property from fully qualified string

2 Answers2

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