FirebaseNotifications.js

function APNStoFCM(token) {
    var body = {
	application : 'com.your.app',
	sandbox : true,
	apns_tokens : [
	    token
	]
    };

    var options = {
	method: "POST",
	headers: {
	    'Accept': 'application/json',
	    "Content-type": "application/json; charset=UTF-8",
	    'Authorization' : 'key=your_key'
	},
	body: JSON.stringify(body)
    }

    fetch("https://iid.googleapis.com/iid/v1:batchImport", options)
	.then(function(response) {
	    return response.json();
	}).then(function(response) {
	    console.log("Prueba " + JSON.stringify(response))
	}).catch(function(error) {
	    console.log("Error " + JSON.stringify(error))
	});
}