How to access a nested key in json using javascript

Question

So, i have this json file, in which i have to take out the fileName tag, and use it.

{
"dataset": {
    "private": false,
    "stdyDscr": {
        "citation": {
            "titlStmt": {
                "titl": "Smoke test",
                "IDNo": {
                    "text": "10.5072/FK2/WNCZ16",
                    ".attrs": {
                        "agency": "doi"
                    }
                }
            },
            "rspStmt": {
                "AuthEnty": "Dataverse, Admin"
            },
            "biblCit": "Dataverse, Admin, 2015, \"Smoke test\", http://dx.doi.org/10.5072/FK2/WNCZ16,  Root Dataverse,  V1 [UNF:6:iuFERYJSwTaovVDvwBwsxQ==]"
        }
    },
    "fileDscr": {
        "fileTxt": {
            "fileName": "fearonLaitinData.tab",
            "dimensns": {
                "caseQnty": "6610",
                "varQnty": "69"
            },
            "fileType": "text/tab-separated-values"
        },
        "notes": {
            "text": "UNF:6:K5wLrMhjKoNX7znhVpU8lg==",
            ".attrs": {
                "level": "file",
                "type": "VDC:UNF",
                "subject": "Universal Numeric Fingerprint"
            }
        },
        ".attrs": {
            "ID": "f6"
        }
    }
},

im using d3.js mostly, but some parts of jquery and javascript with it. right now im doing:

d3.json(url,function(json){ 

              var jsondata=json;

                   var temp = jsondata.dataset.fileDscr.fileTxt.fileName;
}

Is there a way to just access fileName directly? Im asking because, i have to make this generic to fit other json files, where the nesting might be different.

Do you mean you want a method of searching an unknown object structure to get the value associated with a known key name like `"fileName"`? What if the key appears more than once in the object (like `".attrs"` in your example)? (Note also that neither the `json` parameter in your callback nor your `jsondata` variable actually contain JSON, they are both references to the object created by parsing your JSON.) — nnnnnn, Aug 17 '16 at 03:34
Possible duplicate of [Access / process (nested) objects, arrays or JSON](http://stackoverflow.com/questions/11922383/access-process-nested-objects-arrays-or-json) — Nagaraja Thangavelu, Aug 17 '16 at 03:36
you can always write a function that parse the JSON and check for your field or you can stringify your JSON and use regex to extract what ever you need — Basilin Joe, Aug 17 '16 at 03:37
Also, the question title is misleading: "How to access a nested key in json using javascript?"... you're already doing that! — Gerardo Furtado, Aug 17 '16 at 03:38
I'm sorry! I didn't know what to put as the question! this part of the json contains the information about a dataset, so I can safely assum that filename any keys which are there in this segment of the json will occur only once. — Rohit Bhattacharjee, Aug 17 '16 at 16:24

score 1 · Accepted Answer · answered Aug 17 '16 at 03:42

This will return the value for some instance of the key in the JSON data, if it exists.

var data = {...};
function findValue(json, key) {
  if (key in json) return json[key];
  else {
    var otherValue;
    for (var otherKey in json) {
      if (json[otherKey] && json[otherKey].constructor === Object) {
        otherValue = findValue(json[otherKey], key);
        if (otherValue !== undefined) return otherValue;
      }
    }
  }
}
console.log(findValue(data, 'fileName'));

score 0 · Answer 2 · answered Aug 17 '16 at 04:46

It will return a comma separated string of all the values of a specified key

function walk(obj,keyname) {    
    var propertyVal="";                                                                                 
        for (var key in obj) {
            if (obj.hasOwnProperty(key)) {
                var val = obj[key];                                                                                     
                if(typeof(val) == 'object') {
                    console.log(val);                                                                                               
                    propertyVal+= walk(val,keyname);                                                
                }else {
                    if(key == keyname){                                                     
                        propertyVal = propertyVal+","+obj[key];                                                                     
                    }   
                }
            }
        }   
        return propertyVal;                         
}
alert(walk(data,'filename').replace(',',''));

How to access a nested key in json using javascript

2 Answers2