Remove empty properties / falsy values from Object with Underscore.js

Question

I have an object with several properties. I would like to remove any properties that have falsy values.

This can be achieved with compact on arrays, but what about objects?

Solution 1

You could make your own underscore plugin (mixin) :

_.mixin({
  compactObject: function(o) {
    _.each(o, function(v, k) {
      if(!v) {
        delete o[k];
      }
    });
    return o;
  }
});

And then use it as a native underscore method :

var o = _.compactObject({
  foo: 'bar',
  a: 0,
  b: false,
  c: '',
  d: null,
  e: undefined
});

Update

As @AndreiNeculau pointed out, this mixin affects the original object, while the original compact underscore method returns a copy of the array.
To solve this issue and make our compactObject behave more like it's cousin, here's a minor update:

_.mixin({
  compactObject : function(o) {
     var clone = _.clone(o);
     _.each(clone, function(v, k) {
       if(!v) {
         delete clone[k];
       }
     });
     return clone;
  }
});

Solution 2

Since Underscore version 1.7.0, you can use _.pick:

_.pick(sourceObj, _.identity)

Explanation

The second parameter to _.pick can be a predicate function for selecting values. Values for which the predicate returns truthy are picked, and values for which the predicate returns falsy are ignored.

pick _.pick(object, *keys)

Return a copy of the object, filtered to only have values for the whitelisted keys (or array of valid keys). Alternatively accepts a predicate indicating which keys to pick.

_.identity is a helper function that returns its first argument, which means it also works as a predicate function that selects truthy values and rejects falsy ones. The Underscore library also comes with a bunch of other predicates, for instance _.pick(sourceObj, _.isBoolean) would retain only boolean properties.

If you use this technique a lot, you might want to make it a bit more expressive:

var pickNonfalsy = _.partial(_.pick, _, _.identity); // Place this in a library module or something
pickNonfalsy(sourceObj);

Underscore version 1.6.0 provided _.pick as well, but it didn't accept a predicate function instead of a whitelist.

Solution 3

Quick 'n Clear: _.omitBy( source, i => !i );

This is stated in an inverse fashion to Emil's answer. This way imho reads clearer; it's more self explanatory.

Slightly less clean if you don't have the luxury of ES6: _.omitBy( source, function(i){return !i;});

Alternate: _.omitBy( source, _.isEmpty)

Using _.isEmpty, instead of _.identity for truthiness, will also conveniently remove empty arrays and objects from the collection and perhaps inconveniently remove numbers and dates. Thus the outcome is NOT an exact answer to the OP's question, however it could be useful when looking to remove empty collections.

Solution 4

With lodash's transform,

_.transform(obj, function(res, v, k) {
  if (v) res[k] = v;
});

Solution 5

Object.keys(o).forEach(function(k) {
    if (!o[k]) {
        delete o[k];
    }
});

View more solutions

Comments

[Felix Kling]

And one can use underscore for .keys and .forEach.

[Admin]

How would this look in Underscore, then? Trying to piece it together…

[gion_13]

since he wants an underscore solution, you could iterate over the array using one of underscore's methods

[Anton]

+1 this is awesome man. please give me the link of forEach method of JS

[Florian Margaine]

@diEcho developer.mozilla.org/en-US/docs/JavaScript/Reference/…

[Andrei Neculau]

Since the question has an underscore reference, it would be good to mention that this does not behave like _.compact. It will delete properties, rather than create a shallow clone with truthy values only. See stackoverflow.com/a/19750822/465684 below

[gion_13]

@AndreiNeculau You're right! I seem to have missed that earlier. See my updated answer.

[evilive]

whit lodash's _.pick(obj, _.identity); shorter ^_^

[Radko Dinev]

This answer or @evilive's comment under it IS the answer.

[Radko Dinev]

Why first copy all the properties of an object, then loop through them and delete falsy ones? That's unperformant. Moreover, using delete is generally discouraged as it immediately exposes properties with the same name from the prototype chain and also hurts performance due to "hidden classes" (V8) - changing the object structure causes the engine to do extra work. The best and shortest solution would be _.pick(o, _.identity).

[zaboco]

a shorter variation, based on the above comment, would be var compactObject = _.partialRight(_.pick, _.identity);

[ivkremer]

Special thanks for mentioning _.identity function, very handy.

[Ben Patterson]

This has been extremely handy! It's also possible to use _.omit(sourceObj, _.isUndefined) to remove only undefined values (allowing false, null, 0).

[David Chase]

Its also possible to do pick(obj, Boolean) to eliminate falsey values that same approach can be used when arr.filter(Boolean) to clean an array from falsey values...

[Deniz Ozger]

In ES6, this turns into _.pick(sourceObj, prop => prop)

[zooblin]

In lodash 4.4.0 _.pick works with property names, for this functionality as mentioned in post use _.pickBy

[JackMorrissey]

In Lodash 4.0, this functionality is now under omitBy. lodash.com/docs#omitBy

[laggingreflex]

@zaboco In lodash v4 it should be _.pickBy instead of _.pick)

[Turadg]

But it still returns an array. The keys are lost.

[tzvi]

You're right. Do I delete my answer then? Or does stackoverflow prefer something else?

[Turadg]

I don't know a community preference, but if you're fine with leaving it could have value of preventing someone else from adding a similar answer.

[Jeff Lowery]

I believe this is the same as: _.pick(source, i => i); which avoids the negation

[Shibumi]

@JeffLowery This is even better, in Lodash, because the default predicate is the identity function! _.pickBy(source) is all that's needed.

[Jabran Saeed]

0 is not a falsy value. this removes zero as well

[Emil Lundberg]

No, 0 is a falsy value. 0 ? 'true' : 'false' evaluates to 'false'.

[wdetac]

yse, _.pickBy(object) is all you need

[Sir.Nathan Stassen]

Note: Numbers are considered empty. _.isEmpty(5) === true. Thus values that are numbers will be dropped.