JSFiddle - React, Tailwind, and code Playground

JavaScript

Date.prototype.addDays = function(days) {
	var date = new Date(this.valueOf());
	date.setDate(date.getDate() + days);
	return date;
}

function getDates(startDate, stopDate) {
	var dateArray = [];
	var currentDate = startDate;
	while (currentDate <= stopDate) {
		var calendarDay = currentDate.getDate();
		var monthName = new Intl.DateTimeFormat('en-US', options).format(currentDate);
		dateArray.push(calendarDay + " " + monthName);
		currentDate = currentDate.addDays(1);
	}
	return dateArray;
}

var options = { month: 'short' };
var end = new Date();
var start = end.addDays(-7);

var dateArray = getDates(start,end);

let occurences = {
	"19 Dec": 1,
	"21 Dec": 2
};

var copyOcc = occurences;
for(var i = 0; i < dateArray.length; i++) {
	// If the key isn't there, add it
	if(!copyOcc.hasOwnProperty(dateArray[i])) {
		copyOcc[dateArray[i]] = 0;
	}
}

console.log(copyOcc);