Async Iterators for Big Data Sets

    //https://jsonplaceholder.typicode.com/posts
    //retrieves 100 records
    //let's pretend that there are millions of records
    
    let posts = {};
    posts[Symbol.iterator] = function(){
        const URL = "//jsonplaceholder.typicode.com/posts";
        return {
            next: async function(){
                //early pre-emptive move
                let rand = Math.random();
                if(rand > 0.7){
                    return {
                        value: undefined,
                        done: true
                    };
                }
                let request = new Request(URL+`?r=${rand}`, {
                    method: 'GET',
                    mode: 'cors'
                });
                
                let response = await fetch(request);
                //need to add catch()
                let data = await response.json();
                console.log('array of posts fetched', data);
                return {
                    value: data,
                    done: false
                }
            }
        }
    }
    
    let output = document.getElementById('output');
    let main = document.querySelector('main');
    main.addEventListener('click', d);
    
    function d(ev){
        //start getting data
        //output.textContent += JSON.stringify(d);
        let iterator = posts[Symbol.iterator]();
        
        (async function getData(){
            let data = await (iterator.next());
            if(data.value && !data.done){
                output.textContent += '\r\n' + JSON.stringify(data.value);
                console.log('getData', data.value);
                setTimeout(getData, 2000);
            }else{
                console.log( 'Done:', data.done );
                output.textContent += '\r\n DONE.';
            }
        })();
        // IIFE
        //  for await( let val of obj){ }
    }