getting information from a javascript json object

I imagine this has been posted before but I wasn’t able to find a data object specifically like this one. I’m struggling to understand how extract information from this data object in javascript. It’s a parsed URL.

 data =  URL {
  href: 'http://localhost:8080/test.txt?cat=Mouse',
  origin: 'http://localhost:8080',
  protocol: 'http:',
  username: '',
  password: '',
  host: 'localhost:8080',
  hostname: 'localhost',
  port: '8080',
  pathname: '/test.txt',
  search: '?cat=Mouse',
  searchParams: URLSearchParams { 'cat' => 'Mouse' },
  hash: ''
}

I can retrieve the URLsearchParams
data.searchParams, which returns { 'cat' => 'Mouse' }

What is this data structure called: { 'cat' => 'Mouse' }. I’m confused by the =>
And how do I retrieve the two objects ‘cat’ and ‘Mouse’ separately inside this data structure?

For example, retrieving then setting a variable equal to the first item, ‘cat’ and another variable equal to ‘Mouse’

Thank you