Add lesser-known lodash gems to your toolbox - Objects

This is a part two of lodash series.

1. Strings
2. Objects

Removing falsey values from object

I asked from the community to share some lodash/underscore tips and this one got puzzled.

@_Tx3 Return a copy of an object with falsey values removed. _.pick(obj, _.identity);— Jezen Thomas (@jezenthomas) June 5, 2015

Embedded JavaScript

This means that if I'm using object literal like a hashmap:

techCompanies = { 
  nokia: { 
    www: 'nokia.com' 
  },
  apple: undefined,
  motorola: {
    www: 'apple.com'
  }
}

Then I can remove all falsey values from the object like this:

_.pick(techCompanies, _.identity);

> Object {nokia: Object, motorola: Object}

How does it work?

_.pick takes an object as first argument and string/string[]/function as a second argument. Simplest use case could be using _.pick with string argument _.pick(techCompanies, 'apple') and it would return apple object.

In the example we're using _.identity as a second argument and it's a bit mind-confusing little function.

This method returns the first argument provided to it.

The sentence gets me thinking: where's the catch.

But it really is that simple. If null is passed it will return null, if number 2 is passed it will return number 2 and so on.

If _.pick second argument is a function then it will call that function with each property value. It will pick all properties that had function returning true!

Defaults using .assign

This is probably one the most common object related function in lodash and Underscore. With _.assign you can easily copy object properties.

You can have multiple source objects and the rightmost argument will override. Therefore the default value object is normally first source object.

/**
* Create widget to a dashboard.
* @param {Object} widget - The widget that displays beautiful data
* @param {string} widget.name - The name of the widget
*/
Dashboard.prototype.create(widget) {
  var defaults = { 
    name: 'Default name' 
  };
  widget = _.assign({}, defaults , widget);
}

Now when we call .create without name we get default name.

Note: The first argument is destination, but I like to make the variable assign more explicit by using the return value

There is also a function called _.defaults that does this same thing, but with little bit different way of thinking.

_.defaults(widget,  defaults);

Assigns own enumerable properties of source object(s) to the destination object for all destination properties that resolve to undefined. Once a property is set, additional values of the same property are ignored.

One thing to note is that widget is mutated.

For some reason I prefer the first method, it might be just that I'm more used to it or I prefer immutability.

Don't miss commonly used functions such as: _.keys and _.values

What are your favourite object related use of lodash/underscore functions? I would be very happy if you'd share your wisdom to others.