Accessing the web page's HTTP Headers in JavaScript

Question

How do I access a page\'s HTTP response headers via JavaScript?

Related to this question, which was modified to ask about accessing two specific HTTP headers.

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Answer 1

To get the headers as an object which is handier (improvement of Raja's answer):

var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
headers = headers.split(/\n|\r|\r\n/g).reduce(function(a, b) {
    if (b.length) {
        var [ key, value ] = b.split(': ');
        a[key] = value;
    }
    return a;
}, {});
console.log(headers);