Edit in JSFiddle

const data = {
  "dcids": [
		"dc/c3j78rpyssdmf",
		"dc/7hfhd2ek8ppd2"
  ]
}
const request = new XMLHttpRequest();
const firstLine = "dc/c3j78rpyssdmf"
const secondLine = "dc/7hfhd2ek8ppd2"

const writeToDocument = function(line,result) {
	document.write("<h3>In labels</h3>")
	for (let i = 0; i < result[line]["inLabels"].length; i++) {
    let resultName = result[line]["inLabels"][i];
    document.write(resultName + "<br>");
  }
  document.write("<h3>Out labels</h3>")
  for (let i = 0; i < result[line]["outLabels"].length; i++) {
    let resultName = result[line]["outLabels"][i];
    document.write(resultName + "<br>");
  }

}

request.open("POST", "https://api.datacommons.org/node/property-labels", false /* async */ );
request.send(JSON.stringify(data));

if (request.status == 200) {
  let payload = JSON.parse(request.responseText)["payload"];
  let result = JSON.parse(payload);
  console.log(result);
	document.write("<h2>First line of leukocytes:" + firstLine + "</h2>");
  writeToDocument(firstLine,result);
  document.write("<h2>Second line of leukocytes: " + secondLine + "</h2>");
  writeToDocument(secondLine,result);

} else {
  console.log("There was an error fetching data.");
}

<h1>
Property labels of two different leukocyte cell lines
</h1>