AWS.MetadataService is not a constructor

[qq_31239383]

我通过node 在angular集成了aws -sdk，通过
var AWS = require('aws-sdk');
AWS.config.region = 'eu-west-2'; //Sydney
AWS.config.apiVersion = '2012-05-04';
var metadata = new AWS.MetadataService();
metadata.request('/latest/meta-data/iam/security-credentials/', function (err, rolename) {
if (err) {
console.info("err",err);
} else {
console.info("rolename",rolename);
}
});
去得到rolename
但是却报错了，告诉我AWS.MetadataService is not a constructor。
希望谁能告诉一下。
谢谢