var href = "http://c...content-available-to-author-only...b.com/view/qq94";
var xhr = new XMLHttpRequest();
var url = "https://c...content-available-to-author-only...b.com/api/oembed.json?url=" + href.replace(":", "%3A");
//В итоге url == "https://c...content-available-to-author-only...b.com/api/oembed.json?url=http%3A//coub.com/view/qq94"
//Если это вставить в строку браузера, то придет нормальный JSON-ответ
xhr.open("get", url, false);
xhr.send(null);
console.log(xhr.status); //Выводит 0

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