Use the whatwg-fetch polyfil with the aurelia-fetch-client and the aurelia-cli.

Install the polyfil.

npm install whatwg-fetch --save

Preppend the polyfil to the aurelia.json > vendor-bundle.

"bundles": [
  {
    "name": "vendor-bundle.js",
    "prepend": [
      "node_modules/whatwg-fetch/fetch.js",
      "node_modules/bluebird/js/browser/bluebird.core.js",
      "node_modules/requirejs/require.js"
    ],
    "dependencies": [
      "aurelia-binding",
      "aurelia-bootstrapper",
      "aurelia-dependency-injection",
      "aurelia-event-aggregator",
      "aurelia-fetch-client",
      "aurelia-framework",
      "aurelia-history",