Lodash cloneDeepWith to omit undefined

Question

I wrote a customozer function to omit the undefined values of the object with cloneDeepWith. However on the immutable return, it is not digging in recursively.

Answer 1

As far as I know _.cloneDeepWith() customizer is a bit misleading. The customizer should handle only non object values. If it handles object values, it should also continue the recursion by itself. For example, you can see that as the customizer is called, the cloning is handled by value.cloneNode(true). As you can see only body appears in the console.

const { cloneDeepWith, isObject } = _;

function customizer(value) {
  console.log(value);
  if (_.isElement(value)) {
    return value.cloneNode(true);
  }
}
 
var el = _.cloneDeepWith(document.body, customizer);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

However, if you just customize non object values, and return undefined for object values, which prompts the method to handle them (documented in cloneDeep), it iterates everything:

const { cloneDeepWith, isObject, isUndefined } = _;

const obj = {
  a0: true,
  b0: true,
  c0: undefined,
  obj1: {
    a1: true,
    b1: true,
    c1: undefined
  }
};

const result = cloneDeepWith(obj, v => {
  console.log(v);
  
  return isObject(v) ? undefined : 'custom value';
});

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

To solve your problem, you can use _.transform() recursively to take all values that are not undefined:

const { transform, isObject, isUndefined } = _;

const obj = {
  a0: true,
  b0: true,
  c0: undefined,
  obj1: {
    a1: true,
    b1: true,
    c1: undefined
  }
};

const cloneDeepWithoutUndefined = (obj) =>
  transform(obj, (r, v, k) => {
    if(isUndefined(v)) return;
    r[k] = isObject(v) ? cloneDeepWithoutUndefined(v) : v;
  });
  
const result = cloneDeepWithoutUndefined(obj);

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

Answer 2

There's another alternative using DeepDash, which is a standalone, complementary library that offers recursive versions of Lodash functions.

Once DeepDash has been mixed in with Lodash (deepdash(_)), you can write a prune function like this:

const prune = obj => _.filterDeep(obj, (v) => !_.isUndefined(v))

Answer 3

This can be solved by using recursively lodash transform method via:

const obj = { a0: true, b0: true, c0: undefined, obj1: { a1: true, b1: true, c1: undefined } };

const cloneMe = (obj) => _.transform(obj, (r, v, k) => 
  _.isUndefined(v) ? null : _.isObject(v) ? r[k] = cloneMe(v) : r[k] = v, {})

console.log(cloneMe(obj))

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>

You could also do this in ES6 only via Object.entries & reduce:

const obj = { a0: true, b0: true, c0: undefined, obj1: { a1: true, b1: true, c1: undefined } };

const cloneMe = (obj) => {
   return Object.entries(obj).filter(([k,v]) => 
      v != undefined).reduce((r,[k,v]) => {
        r[k] = (v instanceof Object) ? cloneMe(v) : v
        return r
   },{})
}

console.log(cloneMe(obj))

You can additionally extend the check for object if instance of Object is not sufficient etc.