var video = document.createElement('video');

video.onload = function() {

    alert('success, it exsist');

    // show video element

}

video.onerror = function() {

    alert('error, couldn\'t load');

    // don't show video element

}

video.src = 'http://www.example.com/video.mp4';

//不同浏览器情况不同，这里判断在该浏览器是否可以播放

video.oncanplaythrough = function() {

    alert("This file can be played in the current browser");

};

var http = new XMLHttpRequest();

http.open('HEAD', '/folder/video.mp4');

http.onreadystatechange = function() {

    if (this.readyState == this.DONE) {

        if (this.status != ) {

          // resource exists

        }

    }

};

http.send();