讓 js.generator 不斷往下執行

let gseries = require('../node_modules/gseries');

function asynce(index) {
  
    return new Promise(function (res, rej) {
        console.log('index(%s) start', index);
      
        setTimeout(function () {
            console.log('index(%s) end', index);
            res(index);
        }, 3000);
    });
}


function* main() {

    yield asynce(0);

    yield asynce(1);

    return asynce(2);
}


let p = gseries(main);
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/*
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module.exports = gseries;

function gseries(fn, data) {

    return new Promise(function (res, rej) {
        let it = fn();
        job(data);

        //----------------------------
        function job(d) {

            // 主要要不斷重複的步驟
            let g = it.next(d);
            let p = g.value;
            // p.then(...)

            if (g.done) {
                res(p);
            } else if (p instanceof Promise) {
                p.then(function (d) {
                    job(d);
                }, function (err) {
                    rej(err);
                });
            }else{
                job(p);
            }
        }
    });
}