AJAX request to API with callback

AJAXrequest.js

function sendRequest(method, targetURL, content, callback) {
	var http = new XMLHttpRequest(),
	    message = (content !== undefined) ? JSON.stringify(content) : undefined;
	
	http.open(method, targetURL, true);
	
	if (message !== undefined) { /* GET requests may not have JSON content */
		http.setRequestHeader('Content-type', 'application/json; charset=utf-8');
	}

	http.send(message); /* message || undefined */
	
	/* Asynchronous reception */
	http.onreadystatechange = function() {
	    if (http.readyState == 4 && http.status == 200) {
	        return callback(null, http.responseText);
	    } else if (http.status != 200 && http.status != 304) {
	    	return callback(http.status);
	    }
	}
}