wistia.js

       function parentWidth(elem) {
    return elem.parentElement.clientWidth;
}
        var xhr = new XMLHttpRequest();
        var baseUrl = "https://fast.wistia.com/oembed/?url=";
        var accountUrl = encodeURIComponent("https://home.wistia.com/medias/");
        var wistiaId = document.querySelector('.wistia_embed').getAttribute('data-wistia-id');
        console.log("aaa");
        var image_size = parentWidth(document.querySelector(".embed-responsive"));//value in px
        console.log(image_size);
        var thumb_args = 'image_play_button=true&image_play_button_color=7b7968e0&image_resize='+image_size;
        xhr.open('GET',  baseUrl + accountUrl + wistiaId + "&format=json&callback=?");
        xhr.send(null);
        xhr.onreadystatechange = function () {
            var DONE = 4; 
            var OK = 200;
            if (xhr.readyState === DONE) {
                if (xhr.status === OK) 
                var data = JSON.parse(xhr.responseText);
                var thumb = data.thumbnail_url.split('?')[0];
                thumb = thumb + "?" + "image_resize=200";
                var wistcont = document.querySelector("#wistia_" +wistiaId);
                var wistimg = document.createElement("img");
                wistimg.setAttribute("id",'wistia_preview');
                wistimg.setAttribute("src",thumb + "?" + thumb_args);
                wistimg.setAttribute("alt","Couldn't load Wistia video");
                wistimg.classList.add("responsive-img");
                wistcont.appendChild(wistimg);
                wistimg.addEventListener("click",function(){
                    wistiaEmbed = Wistia.embed( wistiaId , {
                        autoPlay: true,
                        controlsVisibleOnLoad: false
                    });
                },false);
                console.log(JSON.parse(xhr.responseText)); 
            } else {
                console.log(xhr.status);
            }
        }