class Scheduler {
constructor () {
this.count = 0
this.waitQueue = [];
}
add(promiseCreator) {
if (this.count < 2) {
this.count += 1;
return this.run(promiseCreator)
} else {
return new Promise(resolve => {
this.waitQueue.push(() => promiseCreator().then(resolve));
})
}
}
run(promiseCreator) {
return promiseCreator().then(() => {
this.count -= 1;
if (this.waitQueue.length) {
this.run(this.waitQueue.shift())
}
});
}
}
const timeout = (time) => new Promise(resolve => {
setTimeout(resolve, time)
})
const scheduler = new Scheduler();
const addTask = (time, order) => {
scheduler.add(() => timeout(time)).then(() => console.log(time, 'time, order', order))
}
addTask(1000, '1');
addTask(500, '2');
addTask(300, '3');
addTask(400, '4');
// output: 2 3 1 4
// 一开始，1、2两个任务进入队列
// 500ms时，2完成，输出2，任务3进队
// 800ms时，3完成，输出3，任务4进队
// 1000ms时，1完成，输出1
// 1200ms时，4完成，输出4
var a = {n:10};
function out(obj){
var b = obj;
var c = b;
b.n = 30;
c = {n : 40};
console.log(a.n);
console.log(b.n);
console.log(c.n);
}
out(a)