Covid-19 Dashboard Tutorial: What is this

1

In step 3 of this tutorial there’s a part that I don’t understand at all and don’t really know how to search for information on it because I haven’t encountered it before.

const geoJson = {
  type: ‘FeatureCollection’,
  features: data.map((country = {}) => {
    const { countryInfo = {} } = country;
    const { lat, long: lng } = countryInfo;
    return {
      type: ‘Feature’,
      properties: {
        …country,
      },
      geometry: {
        type: ‘Point’,
        coordinates: [ lng, lat ]
      }
    }
  })
}

Is this   (country = {}) =>   just assigning country to an empty array if the country parameter is empty ?

And then this  const = { countryInfo = {} } = country  is sort of doing the same thing? But why is it wrapped in brackets?

And the next line confuses me the most   const { lat, long: lng } = countryInfo;

What terms should I use to find more info on this? I just need a starting point because I’m a bit lost.

Thanks in advance!

2

This is destructuring syntax using a default value of an empty object if no property named countryInfo is found in the country object.

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