Fetch some data in javascript code

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Modern javascript has a nice function fetch which uses promises to grab the contents of a url in the background, and then continue when the background process is complete.

Every function which supports promise always has a .then() function, which itself is a promise, so can call its own .then() function, and so on.

Here, we fetch the CMP auto speeds for a specific year, then parse the JSON response, and then run a function on the parsed data:

function colorByLOS(personJson, year) {
  const url = api_server + 'cmp_auto_speeds?year=eq.' + year;

  fetch(url)
  .then((resp) => resp.json())
  .then(function(data) {
    for (let segment in data) {
      // ... do stuff here
    }
  })
  .catch(function(error) {
    console.log(error);
  });
}

Note that after the last .then you need a .catch() to capture any errors.