How to recursively delete a field from an object in javascript ignoring optional fields

Question

I have a an Object and I need to delete all the "id" attributes inside at every deep level except for some of them.

I did this function:

const removeFieldFromObject = ({ obj, fieldName, ignoreFields = [] }) => {
  if (typeof obj !== "object" || obj === null) {
    return obj;
  }

  if (Array.isArray(obj)) {
    for (var i = 0; i < obj.length; i++) {
      obj[i] = removeFieldFromObject({ obj: obj[i], fieldName, ignoreFields });
    }
  } else {
    for (var prop in obj) {
      if (obj.hasOwnProperty(prop)) {
        if (prop === fieldName && !ignoreFields.includes(obj[prop])) {
          delete obj[prop];
        } else {
          obj[prop] = removeFieldFromObject({
            obj: obj[prop],
            fieldName,
            ignoreFields,
          });
        }
      }
    }
  }
  return obj;
};

If i invoke it with this object in the following way:

const obj = {
  id:1,
  data:{
    id:2,
    cards:{
      id:123,
      name:"my name",
      document:{
        id:2,
        url:"my url"
      }
    }
  }
}

const formattedObj = removeFieldFromObject({obj, fieldName: "id", ignoreFields: ["document"]})

It deletes the "id" attribute at all levels

I want it do remove all the attributes "id" except for document objects. This method removes them at every level. The reason is the condition on ignoreFields that is always true when it goes inside the document object and it checks the actual props. I looked around and found many similar questions but not with optional attributes.

Do you have any suggestion? I accept also solutions with lodash or similar.

I need to delete all the "id" attributes can't you just ignore them if you don't need them? — James
– James, Commented Oct 2, 2023 at 15:24

Bergi · Accepted Answer · 2023-10-02 15:25:52Z

1

if (prop === fieldName && !ignoreFields.includes(obj[prop])) {
  delete obj[prop];
} else {
  obj[prop] = removeFieldFromObject(…);
}

This doesn't make a lot of sense - or at least, it doesn't match how you are calling the function. It checks for the value of the property to delete in the ignoreFields. What you actually want is to check the property name before doing the recursive call, so that nothing in .document does get visited:

if (prop === fieldName) {
  delete obj[prop];
} else if (!ignoreFields.includes(prop)) {
  obj[prop] = removeFieldFromObject(…);
}

edited Oct 2, 2023 at 15:25

answered Oct 2, 2023 at 15:20

Bergi

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1 Comment

Loudrous Over a year ago

That's it! Thank you!

Alexander Nenashev · Accepted Answer · 2023-10-02 15:36:55Z

1

Could be something like this:

const removeFieldFromObject = ({obj, fieldName, ignoreFields}) => {

  if(Array.isArray(obj)) {
    arr.forEach(item => removeFieldsFromObject({obj, fieldName, ignoreFields}));
    return;
  }
  if(!Object.prototype.isPrototypeOf(obj)){
    return;
  }
  delete obj[fieldName];
  
  for(const k in obj){
    ignoreFields.includes(k) || removeFieldFromObject({obj: obj[k], fieldName, ignoreFields});
  }
};

removeFieldFromObject({obj, fieldName: "id", ignoreFields: ["document"]})

console.log(obj);

<script>
const obj = {
  id:1,
  data:{
    id:2,
    cards:{
      id:123,
      name:"my name",
      document:{
        id:2,
        url:"my url"
      }
    }
  }
}
</script>

edited Oct 2, 2023 at 15:36

answered Oct 2, 2023 at 15:19

Alexander Nenashev

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9 Comments

Bergi Over a year ago

Better avoid abusing short-circuiting operators for control flow, and avoid the deprecated __proto__

Alexander Nenashev Over a year ago

@Bergi what to use instead of proto? Object.getPrototypeOf() ?

Bergi Over a year ago

Yes, exactly that

Alexander Nenashev Over a year ago

@Bergi isPrototypeOf could be event better i guess

Bergi Over a year ago

What do you actually want to check? For just a primitive/object distinction the OPs typeof obj !== "object" || obj === null is fine (and does not miss undefined, albeit ignoring function objects, which seems sensible). If you want to include function objects, use Object(obj) === obj. Or do you want to check for "plain" objects, i.e. those that don't have a custom prototype like class instances?

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