Call a function before or after the API is fully loaded

I have a button and if it is clicked, I need to call a function that hides another element initialized by a js file that is loaded asynchronously. However, the only way to hide an element is through the Javacsript API. There is no ID or class assigned to the iframe created through the API, so I'm forced to use the JS API for that script.

When my button is clicked, I execute the following code:

if(typeof Tawk_API.hideWidget === "function"){
  Tawk_API.hideWidget();
}else{
  Tawk_API.onLoad = function(){
      Tawk_API.hideWidget();
  };
}

The function successfully hides the widget if the widget is already loaded, or adds onLoad if it is not already loaded.

I know Javascript is not multi-threaded, but is it possible for the processor to hand off the main thread to the middle of my function to load the async js file, which could cause my condition to fail? I want to make sure jsthe file is not loaded during function execution, elsewhich will prevent the script from properly hiding the widget.