fetch-sharepoint.js

var myHeaders = new Headers({
	'X-RequestDigest': document.getElementById('__REQUESTDIGEST').value,
	'Accept': 'application/json; odata=verbose'
})

var myInit = { 
	method: 'GET',
	headers: myHeaders,
	credentials: 'include'
}

fetch(_spPageContextInfo.webAbsoluteUrl + "/_api/web", myInit).then(function(response) {
	if (response.ok) {
		return response.json();
	}
	else {
		throw new Error('Network response was not ok.');
	}
}).then(function(data) {
	if (window.console) {
		console.log(data);
	}
}).catch(function(error) {
	// Error handling code goes here
})