slvn2

is = {
	type: function (value, type) {return {}.toString.call(value).match(/ ([a-z]+)/i)[1] == type}
}

registry = {}

function API_request(method, parameters, success, error) {
	if (!is.type(parameters, "Object")) {
		console.error("parameters must be an object.")

		return
	}

	var callback = "c" + String(Math.random()).slice(-6)
	var flag = false

	registry[callback] =
		function (data) {
			flag = true

			delete registry[callback]

			if (is.type(success, "Function")) {success(data)}
		}

	var URL = "https://api.vk.com/method/" + method + "?"

	for (var key in parameters) {URL += key + "=" + parameters[key] + "&"}

	var script = document.createElement("script")

	script.src = URL + "callback=registry." + callback

	script.onload = script.onerror =
		function () {
			if (flag) {return}

			delete registry[callback]

			if (is.type(error, "Function")) {error()}
		}

	document.head.appendChild(script)
}

API_request(
	"users.get",

	{
		user_ids: "1,2,3",
		fields: "photo_50"
	},

	function (response) {
		for (i = 0; i < response.response.length; i++) {
			img = document.createElement("img")

			img.src = response.response[i].photo_50

			document.body.appendChild(img)
		}
	},

	function () {alert("An error occured. No data loaded.")}
)