How ES6 generators work? Based on http://x-team.com/2015/04/generators-work/

01native-gen.js

/* jshint esnext:true */

// native generators

function* random() {
    var i = 0;
    while(i++ < 1e5) {
        yield Math.random();
    }
}

var rndgen = random();
console.log(rndgen.next());
console.log(rndgen.next());
console.log(rndgen.next());
console.log(rndgen.next());

02es5-gen.js

// fake generators

function random() {
    var i;
    function next(state) {
        while(1) switch(state.prev = state.next) {

        case 0:
            i = 0;

        case 1:
            if(!(i++ < 1e5)) {
                state.next = 4;
                break;
            }
            state.next = 1;
            return Math.random();

        case 4:
        case 'end':
            state.done = true;
            return;

        }
    }

    var state = { next : 0, done : false };
    return {
        next : function() {
            return { value : next(state), done : state.done };
        }
    };
}

var rndgen = random();
console.log(rndgen.next());
console.log(rndgen.next());
console.log(rndgen.next());
console.log(rndgen.next());