How to Use Public JSON APIs

We can query public databases and request data in the form of JSON. To learn about JSON read this
MDN guide to JSON data
JSON: (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate.
API: (Application Program Interface) is a set of routines, protocols, and tools for building software applications. An API specifies how software components should interact.

Open a public JSON API URL in a new tab to see the data.
Example: http://anapioficeandfire.com/api/houses/378
Example: http://anapioficeandfire.com/api/characters/1303
JSON API lists:
https://github.com/toddmotto/public-apis
https://www.programmableweb.com/
https://data.nasa.gov/browse?limitTo=datasets
https://dev.socrata.com/consumers/getting-started.html
https://www.opendatanetwork.com/

Example Code

generic function to request JSON:

function loadJSON(path, success, error) {
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (xhr.readyState === XMLHttpRequest.DONE) {
      if (xhr.status === 200) {
        if (success)
          success(JSON.parse(xhr.responseText));
      } else {
        if (error)
          error(xhr);
      }
    }
  };
  xhr.open("GET", path, true);
  xhr.send();
}

calling the loadJSON function: (replace the URL)

loadJSON('http://api.open-notify.org/iss-now.json',
  function(data) {
    console.log(data)
  },
  function(xhr) {
    console.error(xhr);
  }
);

The JSON data is parsed into an object by the loadJSON function.

data {
  iss_position: {
    latitude: "-41.2572",
    longitude: "-112.0342"
  },
  message: "success",
  timestamp: 1490969278
}