Replacing canvas placeholders with array of external images

I have an array of remote images I want to fetch and pass into user selected placeholders. In the plugin UI I have image data, like…

const data = [ 
   {name: 'One', image: 'https://foo.com/img1.jpg'},
   {name: 'Two', image: 'https://foo.com/img2.jpg'},
]

I understand I need to fetch each one and convert to base64, along the lines of:

  fetch(url)
    .then(r => r.arrayBuffer())
    .then(a => new Uint8Array(a))

and then eventually parent.postMessage(...) with the data. But I don’t know the best way to grab the image data and prepare it to pass it through.