这题 es7 解法!

let sleep = [];

for (var i = 0; i < 5; i++) {
    ((j) => {
        sleep.push(new Promise(function (resolve, reject) {

            setTimeout(function () {
                console.log(new Date, j);
                resolve();
            }, j * 1000)
        }))
    })(i)
}
 // await只能使用在原生语法
(async () => {
    for (let item of sleep) {
        await item
    }
    console.log(new Date(), i);
})();

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