injectScript.js

function injectScript(src) {
  return new Promise(resolve => {
    const e = document.createElement("script");
    e.src = src;
    e.onload = resolve; 
    document.head.appendChild(e);
  });
}

// Example usage
injectScript("https://unpkg.com/axe-core/axe.min.js").then(() => {;
  axe.a11yCheck(document, console.log.bind(console));
});

injectSmartLockScript.js

function injectScript(src) {
  return new Promise(resolve => {
    const e = document.createElement("script");
    e.src = src;
    window.onSmartLockLoad = resolve; 
    document.head.appendChild(e);
  });
}

Minified:

(function (n){return new Promise(function(e){
const t=document.createElement("script");t.src=n,t.onload=e,document.head.appendChild(t)})}
)("https://rawgit.com/ithinkihaveacat/3e72149d5b11277e7c5ab4fa820ee687/raw/paymentRequestMocks.js").then(() => {
showAndSucceed(buildBasicRequest());
});