How to make a JSON object out of getAllResponseHeaders method

Question

I am currently writing a google chrome extension, and I need to find out information about websites' response headers. In order to do this, I used the getAllResponseHeaders method, but I need to put it in a JSON object. Unfortunately, I keep getting the error message SyntaxError: Unexpected token D in JSON at position 0 at main.

Here is the code I am using to do this so far:

xmlhttp.open("GET", url, false);
xmlhttp.onreadystatechange=function() {
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        allResponseHeaders = xmlhttp.getAllResponseHeaders();
    }
};
xmlhttp.send();

var responseHeaders = JSON.parse(allResponseHeaders);
obj.headers = responseHeaders;

When I put an alert immediately after the allResponseHeaders = xmlhttp.getAllResponseHeaders(); call, the alert shows that the call was a success; the response headers have all been retrieved. The first response header is the Date, which I think has to do with the Unexpected token D part of my error message, but I don't know why it won't parse properly. How do I fix this? Thanks in advance.

EDIT: I would like my JSON object to look something like this:

{
  "headers": {
    "Date": "June 20, 2016",
    "Content-Type": "charset=UTF/8",
    ...
  }
}

Answer 1

See https://msdn.microsoft.com/en-us/library/ms536428(v=vs.85).aspx. The return headers are a crlf delimited string where each line contains key values separated by a colon. You will probably have to adjust the code below to account for whitespace.

var arr = allResponseHeaders.split('\r\n');
var headers = arr.reduce(function (acc, current, i){
      var parts = current.split(': ');
      acc[parts[0]] = parts[1];
      return acc;
}, {});