let responseJSON;
try{
	const response = await fetch('/Something/YourURL', {
		method: 'POST', 
		body: JSON.stringify({}),
		headers: { 'Content-Type': 'application/json', 'X-Requested-With': 'fetch' }
	});
	//if(!response.ok) throw new Error(`Error processing request: ${response.statusText}`);
	responseJSON = await response.json();
}catch(error){
	console.error(error);
	// error function here
}

if(responseJSON){
	if(responseJSON.Success) // successful function here
	else //error function here
}