CODEWITHSUNDEEP
node.jsjson
trent
trent

Reputation: 23

How do I filter keys from JSON in Node.js?

I'm trying to select certain keys from an JSON array, and filter the rest.

var json = JSON.stringify(body);

which is:

{  
   "FirstName":"foo",
   "typeform_form_submits":{  
      "foo":true,
      "bar":true,
      "baz":true
   },
  "more keys": "foo",
  "unwanted key": "foo"
}

Want I want:

{  
   "FirstName":"foo",
   "typeform_form_submits":{  
      "foo":true,
      "bar":true,
      "baz":true
   }
}

I've checked out How to filter JSON data in node.js?, but I'm looking to do this without any packages.

Upvotes: 2

Views: 5116

Answers (4)

NerdyDeeds
NerdyDeeds

Reputation: 469

I know this question was asked aways back, but I wanted to just toss out there, since nobody else did:

If you're bound and determined to do this with stringify, one of its less-well-known capabilities involves replacer, it's second parameter. For example:

// Creating a demo data set
let dataToReduce = {a:1, b:2, c:3, d:4, e:5};
console.log('Demo data:', dataToReduce);

// Providing an array to reduce the results down to only those specified.
let reducedData = JSON.stringify(dataToReduce, ['a','c','e']);
console.log('Using [reducer] as an array of IDs:', reducedData);

// Running a function against the key/value pairs to reduce the results down to those desired.
let processedData = JSON.stringify(dataToReduce, (key, value) => (value%2 === 0) ? undefined: value);
console.log('Using [reducer] as an operation on the values:', processedData);

// And, of course, restoring them back to their original object format:
console.log('Restoration of the results:', '\nreducedData:', JSON.parse(reducedData), '\nprocessedData:', JSON.parse(processedData));

In the above code snippet, the key value pairs are filtered using stringify exclusively:

  • In the first case, by providing an array of strings, representing the keys you wish to preserve (as you were requesting)
  • In the second, by running a function against the values, and dynamically determining those to keep (which you didn't request, but is part of the same property, and may help someone else)
  • In the third, their respective conversions back to JSON (using .parse()).

Now, I want to stress that I'm not advocating this as the appropriate method to reduce an object (though it will make a clean SHALLOW copy of said object, and is actually surprisingly performant), if only from an obscurity/readability standpoint, but it IS a totally-effective (and mainstream; that is: it's built into the language, not a hack) option/tool to add to the arsenal.

Upvotes: 0

doron
doron

Reputation: 261

Now you can use Object.fromEntries like so:

Object.fromEntries(Object.entries(raw).filter(([key]) => wantedKeys.includes(key)))

Upvotes: 5

Varun Suresh Kumar
Varun Suresh Kumar

Reputation: 879

var raw = {  
   "FirstName":"foo",
   "typeform_form_submits":{  
      "foo":true,
      "bar":true,
      "baz":true
   },
  "more keys": "foo",
  "unwanted key": "foo"
}
var wantedKeys =["FirstName","typeform_form_submits" ]
var opObj = {}
Object.keys(raw).forEach( key => {
   if(wantedKeys.includes(key)){
    opObj[key] = raw[key]
 }
})

console.log(JSON.stringify(opObj))

Upvotes: 1

remix23
remix23

Reputation: 3019

You need to filter your obj before passing it to json stringify:

const rawJson = {  
   "FirstName":"foo",
   "typeform_form_submits":{  
      "foo":true,
      "bar":true,
      "baz":true
   },
  "more keys": "foo",
  "unwanted key": "foo"
};

// This array will serve as a whitelist to select keys you want to keep in rawJson
const filterArray = [
  "FirstName",
  "typeform_form_submits",
];

// this function filters source keys (one level deep) according to whitelist
function filterObj(source, whiteList) {
  const res = {};
  // iterate over each keys of source
  Object.keys(source).forEach((key) => {
    // if whiteList contains the current key, add this key to res
    if (whiteList.indexOf(key) !== -1) {
      res[key] = source[key];
    }
  });
  return res;
}

// outputs the desired result
console.log(JSON.stringify(filterObj(rawJson, filterArray)));

Upvotes: 2

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