I have javascript objects which looks similar to this:

{
  id: 43,
  name: 'ajajaj'
  nestedObj1: {
    id: 53,
    name: 'ababab'
    foo: 'xxxx'
    nestedObj2: {
      id: 90,
      name: 'akakaka'
      foo2: 'sdsddd'
      surname: 'sdadasd'
      nestedObj3: {
        id: ..
        name: ..
        ...
      },
      objectsArr: [
        {id: .., name: ..., nestedOb4: {...} },
        {id: .., name: ..., nestedOb4: {...} }
      ]
    },
    foo0: ...
  }
  name: 'blabla'
}

Each objects which I have, has property id and name. My goal is pick all properties in first level, so properties of object with id 43 I pick all, and from every nested objects, I just pick properties id and name, and another will be thrown away.

I am using in project lodash, so I found function pick, but I don't know how to use this function for nested objects. Also note that nested objects could be also in array. Exist some elegant way for that please? Thanks in advice.

I have javascript objects which looks similar to this:

{
  id: 43,
  name: 'ajajaj'
  nestedObj1: {
    id: 53,
    name: 'ababab'
    foo: 'xxxx'
    nestedObj2: {
      id: 90,
      name: 'akakaka'
      foo2: 'sdsddd'
      surname: 'sdadasd'
      nestedObj3: {
        id: ..
        name: ..
        ...
      },
      objectsArr: [
        {id: .., name: ..., nestedOb4: {...} },
        {id: .., name: ..., nestedOb4: {...} }
      ]
    },
    foo0: ...
  }
  name: 'blabla'
}

Each objects which I have, has property id and name. My goal is pick all properties in first level, so properties of object with id 43 I pick all, and from every nested objects, I just pick properties id and name, and another will be thrown away.

I am using in project lodash, so I found function pick, but I don't know how to use this function for nested objects. Also note that nested objects could be also in array. Exist some elegant way for that please? Thanks in advice.

• javascript
• lodash

2 Answers 2

pick function of lodash is able to fetch nested property like so:

_.pick(obj, [
  'id',
  'name',
  'nestedObj1.id',
  'nestedObj1.name',
  'nestedObj1.nestedObj2.id',
  'nestedObj1.nestedObj2.name',
  'nestedObj1.nestedObj2.nestedObj3.id',
  'nestedObj1.nestedObj2.nestedObj3.name',
  'nestedObj1.nestedObj2.objectsArr[0].id',
  'nestedObj1.nestedObj2.objectsArr[0].name',
  'nestedObj1.nestedObj2.objectsArr[0].nestedObj4.id',
  'nestedObj1.nestedObj2.objectsArr[0].nestedObj4.name',
  'nestedObj1.nestedObj2.objectsArr[1].id',
  'nestedObj1.nestedObj2.objectsArr[1].name',
  'nestedObj1.nestedObj2.objectsArr[1].nestedObj4.id',
  'nestedObj1.nestedObj2.objectsArr[1].nestedObj4.name',
])

The problem is, you must know the array length to pick all objects in them.

To mitigate this, you can use this function to iterate over arrays:

const _ = require('lodash')

const pickExtended = (object, paths) => {
  return paths.reduce((result, path) => {
    if (path.includes("[].")) {
      const [collectionPath, itemPath] = path.split(/\[]\.(.+)/);
      const collection = _.get(object, collectionPath);

      if (!_.isArray(collection)) {
        return result;
      }

      const partialResult = {};
      _.set(
        partialResult,
        collectionPath,
        _.map(collection, item => pickExtended(item, [itemPath]))
      );

      return _.merge(result, partialResult);
    }

    return _.merge(result, _.pick(object, [path]));
  }, {});
};

You can then get the result you want with:

pickExtended(obj, [
  'id',
  'name',
  'nestedObj1.id',
  'nestedObj1.name',
  'nestedObj1.nestedObj2.id',
  'nestedObj1.nestedObj2.name',
  'nestedObj1.nestedObj2.nestedObj3.id',
  'nestedObj1.nestedObj2.nestedObj3.name',
  'nestedObj1.nestedObj2.objectsArr[].id',
  'nestedObj1.nestedObj2.objectsArr[].name',
  'nestedObj1.nestedObj2.objectsArr[].nestedObj4.id',
  'nestedObj1.nestedObj2.objectsArr[].nestedObj4.name',
])

Here is the associated mocha test:

describe("pickExtended", () => {
  const object = {
    a: 1,
    b: "2",
    c: { d: 3, e: 4 },
    f: [
      { a: 11, b: 12, c: [{ d: 21, e: 22 }, { d: 31, e: 32 }] },
      { a: 13, b: 14, c: [{ d: 23, e: 24 }, { d: 33, e: 34 }] }
    ],
    g: [],
    h: [{ a: 41 }, { a: 42 }, { a: 43 }]
  };

  it("should pick properties in nested collection", () => {
    expect(
      pickExtended(object, ["a", "c.d", "f[].c[].d", "g[].a", "b[].a", "h[]"])
    ).to.deep.equal({
      a: 1,
      c: { d: 3 },
      f: [{ c: [{ d: 21 }, { d: 31 }] }, { c: [{ d: 23 }, { d: 33 }] }],
      g: []
    });
  });
});

Keep in mind that no performance test was done on this. It might get slow for big object.

You can do this using recursion, as long as your objects do have an end to the levels of nesting. Otherwise, you run the risk of causing a stack limit error.

function pickProperties(obj) {
    var retObj = {};
    Object.keys(obj).forEach(function (key) {
        if (key === 'id' || key === 'name') {
            retObj[key] = obj[key];
        } else if (_.isObject(obj[key])) {
            retObj[key] = pickProperties(obj[key]);
        } else if (_.isArray(obj[key])) {
            retObj[key] = obj[key].map(function(arrayObj) {
                return pickProperties(arrayObj);
            });
        }
    });
    return retObj;
}