Edit in JSFiddle

const request = new XMLHttpRequest();
request.open("GET", "https://api.datacommons.org/stat/series?place=country%2FBIH&stat_var=Count_Person&measurement_method=BosniaCensus", false /* async */ );
request.send();

if (request.status == 200) {
  let result = JSON.parse(request.responseText);
  console.log(result);
  let resultSeries = result['series'];
  for (const [key, value] of Object.entries(resultSeries)) {
  	let keyValueOutput = key + ": " + value + "<br />";
  	document.write(keyValueOutput);
	}
} else {
  console.log("There was an error fetching data.");
}

<p>
  Count of people in <a href="https://api.datacommons.org/stat/series?place=country%2FBIH&stat_var=Count_Person&measurement_method=BosniaCensus">Bosnia</a> according to the Bosnia Census: <span id="result"></span>
</p>