Callbacks vs. Promises

callbacks-vs-promises.js

// GET with callbacks

function get(url, success, error) {
	var ajax = new XMLHttpRequest();

	ajax.onreadystatechange = function() {
		if (this.readyState === 4) {
			if (this.status === 200) {
			  var result = JSON.parse(this.responseText);
			  success(result);
			} else {
			  error(this.responseText);
			}				
		}
	}

	ajax.open('GET', url);
	ajax.send();	
}

get('https://www.reddit.com/.json', function(result) {
	console.log(result);
}, function(error) {
	console.log(error);
});

// GET with promises

function get(url) {
	return new Promise(function(resolve, reject){
		var ajax = new XMLHttpRequest();

		ajax.onreadystatechange = function() {
			if(this.readyState === 4) {
				if (this.status === 200) {
				  var result = JSON.parse(this.responseText);
				  resolve(result);
				} else {
				  reject(this.statusText)
				}			
			}
		}

		ajax.open('GET', url);
		ajax.send();	
	});
}

get('https://www.reddit.com/.json').then(function(result) {
	console.log(result);
}).catch(function(error){
	console.log(error);
});