High Order Function

var Type = {}

for(var i =0, type; type =['String','Array','Number'][i++];){
    (function(type){
        Type['is'+type] = function(obj){
            return Object.prototype.toString.call(obj) === '[object ' + type + ']';
        }
    })(type)

};

Type.isArray([]);
Type.isString('abc');

var getSingle = function(fn){
	var ret;
	return function(){
		return ret || (ret = fn.apply(this, arguments));
	};
};

var getScript = getSingle(function(){
	return document.createElement('script'):
})

var script1 = getScript();
var script2 = getScript();
console.log(script1 === script2);