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Destructuring Objects in ES6

2018-03-04 Tiffany WhiteES6

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What is destructuring?

Destructuring is a way to extract values from nested arrays and objects.

When you use destructuring, you are taking a JavaScript expression and extracting data from either arrays, objects, maps, and sets into their own variable. It also allows you to extract properties on an object or items from an array in multiples.

Examples

const car = {
  make: 'Subaru',
  model: 'BRZ',
  year: '2018',
  dealership: 'Cochran',
  city: 'Pittsburgh'
};

const make = car.make;
const model = car.model;

In this example, we have some pretty repetitive code where we need to create a variable from some value inside of an object.

Instead of creating multiple variables, we can destructure them to a single, sweet line:

const { make, model } = car;

where we get a variable called make and a variable called model extract them from the car object and putting them into their own variables which are scoped to the parent block, in this case, the window since they aren’t in a nested object.

If I wanted to add another property to the destructured object, I could do something like this:

const { make, model, year } = car;

where we get a top level variable inside our scope.

This is a good use of destructuring, but what if we want to get at data in nested arrays and objects?

Take this data we get from some web API:

const weather = {
  city: 'Pittsburgh',
  state: 'Pennsylvania',
  local: {
    precipitation: {
      snowing: yes,
      raining: no,
    },
    coordinates: {
      lat: '40.4406° N',
      long: '79.9959° W'
    }
  }
};

I just want the latitude and longitude in this case. I could do:

const lat = weather.local.coordinates.lat;
const long = weather.local.cooridinates.long;

but this is not easy to reason about.

Destructuring to the rescue:

const { lat, long } = weather.local.coordinates;
console.log(lat, long);

In this instance we need to destructure weather.local.coordinates because we are destructuring an object a few levels deep.

Other Fun Stuff

You can also rename and destructure variables in ES6.

How?

const snowing = 'no';
const weather = {
  city: 'Pittsburgh',
  state: 'Pennsylvania',
  local: {
    precipitation: {
      snowing: 'yes',
      raining: 'no',
    },
    coordinates: {
      lat: '40.4406° N',
      long: '79.9959° W'
    }
  }
};

Here I already have a snowing variable. I also have a snowing key on the same object. You aren’t able to do this, however, so you will need to rename the variable or the key within the object. In this instance, we can rename the snowing property to snow and the raining property to rain.

const { snowing: snow, raining: rain } = weather.local.precipitaton;

This will assign weather.local.precipitaton to a variable called snow and also to a variable called rain.

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