const SiteClient = require('datocms-client').SiteClient;
const client = new SiteClient('YOUR-API-TOKEN');
client.uploadRequest.create({
  filename: 'image.png'
})
.then((uploadRequest) => {
  console.log(uploadRequest);
})
.catch((error) => {
  console.error(error);
});

> node example.js
{
  "id": "/7/1455102967-image.png",
  "url": "https://dato-images.s3-eu-west-1.amazonaws.com/7/1455102967-image.png?X-Amz-Credential=AKIAJDTXTZHHDUCKAUMA%2F20160210"
}