youtubeToSpotify.js

// ==UserScript==
// @name          YouSpotify
// @author        doruk
// @description   Adds a play on spotify button
// @include       http://*.youtube.com/watch?*v=*
// @include       http://*.youtube.com/watch#!*v=*
// @include       http://youtube.com/watch?*v=*
// @include       http://youtube.com/watch?v=*
// @include       http://youtube.com/watch#!*v=*
// @include       http://www.youtube.com/user/*
// @include       https://*.youtube.com/watch?*v=*
// @include       https://*.youtube.com/watch#!*v=*
// @include       https://youtube.com/watch?*v=*
// @include       https://youtube.com/watch?v=*
// @include       https://youtube.com/watch#!*v=*
// @include       https://www.youtube.com/user/*
// @include       http://*.youtube.com/watch%3F*v=*
// @version       1
// ==/UserScript==

var title = document.getElementById("eow-title").innerText.replace('/\([^)]*\)/', "");

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == XMLHttpRequest.DONE ) {
        if(xmlhttp.status == 200){
            var data = JSON.parse(xmlhttp.responseText);
            var id = data["tracks"]["items"][0]["id"];

            var e = document.createElement('iframe');
                e.src = "https://embed.spotify.com/?uri=spotify:track:" + id;
                e.width = "100%";
                e.height = 80;
                e.frameborder = 0;
                e.allowtransparency = true;

            document.getElementById("watch-description-clip").insertBefore(e, document.getElementById("watch-description-clip").childNodes[0]);
        }
        else {
            console.log('something else other than 200 was returned. code: ' + xmlhttp.status);
        }
    }
}

xmlhttp.open("GET", "https://api.spotify.com/v1/search?q=" + title + "&type=track", true);
xmlhttp.send();