How can I download a file from the Box API using client-side javascript?  I've tried the following:

var url = 'https://api.box.com/2.0/files/file_id/content';

var xhr = new XMLHttpRequest();

xhr.open('GET', url);

xhr.setRequestHeader('Authorization', 'Bearer '+my_token);

xhr.onload = function()

{

	//stuff

}

xhr.onerror = function()

{

        //more stuff

}

xhr.send();

When the request is made, though, the following error is thrown: 

XMLHttpRequest cannot load https://api.box.com/2.0/files//content. The request was redirected to 'https://dl.boxcloud.com/d/1/.../download', which is disallowed for cross-origin requests that require preflight.