How to parse JSON having nested arrays in javascript or jquery

Question

I want to parse JSON like below

{
   "nodeId":3892718504,
   "root":true,
   "subs":[
      {
         "nodeId":3892717286
      },
      {
         "nodeId":3892716092,
         "subs":[
            {
               "nodeId":3892715856,
               "subs":[
                  {
                     "nodeId":3892718592,
                     "subs":[
                        {
                           "nodeId":3892717580
                        }
                     ]
                  }
               ]
            }
         ]
      },
      {
         "nodeId":3892717497
      }
   ]
}

Each node can have subs and those subs can have nodes that can have their own subs. all I want is an array having all nodeId, how can I parse this JSON such that an array called nodes_list is populated with all nodeId. I can use javascript or jquery.

I'm trying the following approach to get an array of nodeId

jQuery.each(response.topology, function(i,obj) {
  if(i == "nodeId") {
    node_list.push(obj)
  }
  if(i == "subs"){
    jQuery.each(i, function(key,value) {
        if(i == "nodeId") {
            node_list.push(obj)
        }
    }
  }
});

I just need a little hint on how it can be in an iterative manner.

Can you please show us what you've tried to accomplish that task? — briosheje
– briosheje, Commented Jun 18, 2019 at 12:03
You seem to be confusing "parsing" with "transforming the parsed data structure into a different data structure". You also don't seem to have made any effort or done any research on how to do this. — Quentin
– Quentin, Commented Jun 18, 2019 at 12:04
please I know I'm silly to ask such question but all I need is loop that checks for subs in each iteration and — Rishabh Gusain
– Rishabh Gusain, Commented Jun 18, 2019 at 12:12

briosheje · Accepted Answer · 2019-06-18 12:15:10Z

4

This can be done with function generators.

Perhaps not the most enjoyable approach, but I'm pretty sure the other solutions will already imply using other ways, so here is a solution using generators.

PS: Beware of browser support: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/yield

const input = {
   "nodeId":3892718504,
   "root":true,
   "subs":[
      {
         "nodeId":3892717286
      },
      {
         "nodeId":3892716092,
         "subs":[
            {
               "nodeId":3892715856,
               "subs":[
                  {
                     "nodeId":3892718592,
                     "subs":[
                        {
                           "nodeId":3892717580
                        }
                     ]
                  }
               ]
            }
         ]
      },
      {
         "nodeId":3892717497
      }
   ]
};

function* nodeLookup(obj) {
  if (obj.nodeId) yield obj.nodeId;
  if (obj.subs) for (var i = 0; i < obj.subs.length; i++) yield *nodeLookup(obj.subs[i]);
};

const node_ids = [...nodeLookup(input)];
console.log(node_ids);

answered Jun 18, 2019 at 12:15

briosheje

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4 Comments

Rishabh Gusain Over a year ago

that seems to be the only solution that will do for now, Thank you so much without your help I would have stuck forever on extracting data from nested loops. I'm also sorry for not posting my fail attempts to the problem on the first.

briosheje Over a year ago

@RishabhGusain you can avoid using function generators by just using the (already available above) recursion. I've decided to follow the function* apporach because you can easily wrap the result according to your need (in that case, the spread operator ... is used to accumulate the function generator's results in an array). If you want to, you can transform the above code by removing the function generators and adding an accumulator manually.

Scott Sauyet Over a year ago

@RishabhGusain: it's fine that you didn't post your attempt this time since you went back and added it... if you learn from this and remember to do so in the future.

Attersson Over a year ago

This approach best complies with modern Javascript

Adams Hales · Accepted Answer · 2019-06-18 12:23:51Z

2

Just use recursion to iterate over subs

var nodeIds = [];
if (data.nodeId) nodeIds.push(data.nodeId);
function fetchNodeIds (subs) {
    if (!subs.length) return cb([]);
    var abc = [];
    subs.forEach(function (sub) {
        abc.push(sub.nodeId);
        if (sub.subs && sub.subs.length) abc = abc.concat(fetchNodeIds(sub.subs))
    });
    return abc;
}
nodeIds = nodeIds.concat(fetchNodeIds(data.subs));
console.log('--All nodeIds--', nodeIds)

answered Jun 18, 2019 at 12:23

Adams Hales

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1 Comment

Scott Sauyet Over a year ago

Sure, but see my answer for a simpler recursion.

Scott Sauyet · Accepted Answer · 2019-06-18 12:29:54Z

It's straightforward to do recursively:

const gatherIds = ({nodeId, subs}, results = []) => subs
  ? [...results, nodeId, ...(subs .flatMap (sub => gatherIds (sub, results) ))]
  : [...results, nodeId]

const response = {"nodeId": 3892718504, "root": true, "subs": [{"nodeId": 3892717286}, {"nodeId": 3892716092, "subs": [{"nodeId": 3892715856, "subs": [{"nodeId": 3892718592, "subs": [{"nodeId": 3892717580}]}]}]}, {"nodeId": 3892717497}]}

console .log (
  gatherIds (response)
)

If your target environments don't support flatmap, it's easy enough to shim.

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