function guidMaker(){

    function generator() {
		    const S4 = () => (((1+Math.random())*0x10000)|0).toString(16).substring(1);
		    return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
		}

		const done = false;
		let generated = 0;

    return {
       next: function() { return { value: generator(), done, generated: ++generated } }
    };
}

var guid = guidMaker();

console.log( JSON.stringify(guid.next()) );
console.log( JSON.stringify(guid.next()) );
console.log( JSON.stringify(guid.next()) );