Value testing functions

testers.js

function existy(val) {
	return val !== undefined && val !== null && !isRealNaN(val);
}

function toClass(obj) {
	return Object.prototype.toString.call(obj);
}

function isMaker(type) {
	return function(val) {
		return toClass(val).slice(8, -1) === type;
	}
}

var isFunction = isMaker('Function');

var isString = isMaker('String');

var isNumber = isMaker('Number');

var isArguments = isMaker('Arguments');

function isRealNaN(val) {
	return isNumber(val) && val != +val;
}