Let a script loaded before Intercom wait until intercom has booted

script.js

function afterIntercom() {
  if (window.intercomSettings.is_intercom_bubble_enabled && window.intercomSettings.is_intercom_twoway_enabled) {
    // do something
  }
}

if (window.intercomSettings) {
  afterIntercom();
} else {
  Object.defineProperty(window, 'intercomSettings', {
    configurable: true,
    enumerable: true,
    get: function() {
      return this._intercomSettings;
    },
    set: function(val) {
      this._intercomSettings = val;
      afterIntercom();
    }
  });
}

This approach is safer. At the very beginning, intercom might be undefined and ultimately break the app
if (!!window.Intercom && window.Intercom.booted)

In the call to Object.defineProperty, the option

writeable: true,

should be eliminated. When using the correctly spelled option, writable: true, it is considered an error to have accessors and writable at the same time:

TypeError: Invalid property descriptor. Cannot both specify accessors and a value or writable attribute