Class ExposedPromise<T>

let task_a = ExposedPromise.create();
let task_b = ExposedPromise.create();

let taskGroup = Promise.all([task_a.ins, task_b.ins]);
taskGroup.then(() => {
    console.log("all finish!");
});

task_a.ins.then(() => {
    console.log("task a finish");
})

task_b.ins.then(() => {
    console.log("task b finish");
})

setTimeout(() => task_a.resolve(), 1000);
setTimeout(() => task_b.resolve(), 3000);