Asynchronous script to call flickr API via JavaScript, displays photos from a flickr set

flickr.js

var flickr = {
	apiKey: null,
	photosetId: null,
	photos: null,
	limit: null,
	url: null,
	async: false,
	elementId: false,
	init: function(apiKey, photosetId, limit, async, elementId) {
		this.apiKey = apiKey;
		this.photosetId = photosetId;
		this.url = 'https://api.flickr.com/services/rest/?method=flickr.photosets.getPhotos&api_key='+this.apiKey+'&photoset_id='+this.photosetId+'&format=json&extras=url_m',
		this.limit = parseInt(limit);
		this.async = async;
		this.elementId = elementId;

		// options passed to callback later
		var options = {
			limit: this.limit,
			photosetId: this.photosetId,
			async: this.async,
			elementId: this.elementId
		}

		// passing callback to handle async http call
		this.httpGet(this.url, this.getPhotos, options);
		return this;
	},
	jsonFlickrApi : function(code) {
		return code;
	},
	getPhotos : function(response, options) {
		var execute = 'flickr.'+response;
		var object = eval(execute);
		flickr.write(object, options);
	},
	httpGet: function(url, callback, options) {
		var xmlHttp = null;
		xmlHttp = new XMLHttpRequest();
		xmlHttp.open("GET", url, this.async);
		xmlHttp.onload = function (e) {
			if (xmlHttp.readyState === 4) {
				if (xmlHttp.status === 200) {
					callback(xmlHttp.responseText, options);
				}
			}
		}
		xmlHttp.send(null);
	},
	getRandomNumber: function(base) {
		return Math.floor((Math.random() * (base)) + 1);
	},
	write: function(object, options) {
		var photos = [];

		object.photoset.photo.forEach(function(element){
			photos.push([element.url_m, element.title]);
		});

		var html = '';

		for (var i = 0; i < this.limit; i++) {
			var random = this.getRandomNumber(photos.length -1);
			html += '<img src="'+photos[random][0]+'" alt="'+photos[random][1]+'" />';
		}

		var flickrUrl = 'https://www.flickr.com/photos/'+object.photoset.ownername.toLowerCase()+'/sets/'+options.photosetId+'/';
		html += '<p class="taken_from">Random '+options.limit+' photos taken from <a href="'+flickrUrl+'" target="_blank">'+flickrUrl+'</a></p>';

		html += '';
		var element = document.getElementById(options.elementId);
		element.innerHTML = html;
	}
}

document.write('<div id="flickr"></div>');
flickr.init('50b2c88d16b7d6765f8c2f9b9bce844f', '72157644508338618', 4, true, 'flickr');