EXT_disjoint_timer_query.getQueryObjectEXT()

getQueryObjectEXT(query, pname)

var ext = gl.getExtension('EXT_disjoint_timer_query');
var query = ext.createQueryEXT();
ext.beginQueryEXT(ext.TIME_ELAPSED_EXT, query);

// ... drawing ...

ext.endQueryEXT(ext.TIME_ELAPSED_EXT);

// At some point in the future, after returning control to the browser
var available = ext.getQueryObjectEXT(query, ext.QUERY_RESULT_AVAILABLE_EXT);
var disjoint = gl.getParameter(ext.GPU_DISJOINT_EXT);

if (available && !disjoint) {
  // See how much time the rendering of the object took in nanoseconds.
  var timeElapsed = ext.getQueryObjectEXT(query, ext.QUERY_RESULT_EXT);
}