Get result of functions run in window context

main.js

import * as windowContextRunner from './windowContextRunner.js'

windowContextRunner.run(function() {
  // Do something and return the result
  var result = 1;
  return result;
}).then(function(result) {
  // Use the result of the function above
  result == 1
});

windowContextRunner.js

'use strict'

let waitScriptResult = function (id, timeout) {
  return new Promise(function (resolve, reject) {
    let timerId
    timerId = setInterval(function () {
      let elem = document.getElementById(id)
      if (typeof elem !== 'undefined' && typeof elem.dataset.done !== 'undefined') {
        clearInterval(timerId)
        timerId = null
        if (typeof elem.dataset.error !== 'undefined' && elem.dataset.error !== '') {
          reject(Error(elem.dataset.error))
        } else {
          resolve(JSON.parse(elem.dataset.result))
        }
        document.body.removeChild(elem)
      }
    }, 100)
    setTimeout(function () {
      if (timerId) {
        clearInterval(timerId)
        reject(Error('The injected script was timeout'))
      }
    }, timeout || 5000)
  })
}

let injectScript = function (promise) {
  let n = Math.floor(Math.random() * 1000000)
  let id = `kzaex_run_in_page_${n}`
  let s = document.createElement('script')
  s.id = id
  s.text = `
    (function() {
      var promise = ${promise.toString()};
      var script = document.getElementById("${id}");
      promise.then(function(result, reject) {
        script.dataset.result = JSON.stringify(result);
        script.dataset.done = 'true';
      }).catch(function(e) {
        script.dataset.error = e.message;
        script.dataset.done = 'true';
      })
    })();
    `
  document.body.appendChild(s)
  return id
}

export function run (script, timeout) {
  let id = injectScript(`
    new Promise(function(resolve, reject) {
      try {
        resolve((${script.toString()})());
      } catch(e) {
        reject(e);
      }
    });
    `)
  return waitScriptResult(id, timeout)
}

export function runWithCallback (script, timeout) {
  let id = injectScript(`
    new Promise(function(resolve, reject) {
      try {
        (${script.toString()})(function(result) {
          resolve(result);
        });
      } catch(e) {
        reject(e);
      }
    });
  `)
  return waitScriptResult(id, timeout)
}