请教node.js中promise的使用方法

[雨中的月儿]

代码如下：

var _ = require("./underscore");

var arr = [1,2,3,4,5];
var startPromise = new Promise(function(resolve, reject) {
    resolve(1000);
});

var chainPromise = startPromise;

var startDate = Date.now();
_.each(arr, function (val) {
    chainPromise = chainPromise.then(function(ret) {
        console.log("No." + val + ", " + ret);
        return startPromise;
    });
});
var timeSpan = new Date() - startDate;
console.log("Finished , " + timeSpan + "ms");

我期望的输出结果是：
No.1, 1000
No.2, 1000
No.3, 1000
No.4, 1000
No.5, 1000
Finished , 1ms

但实际的结果是：
Finished , 1ms
No.1, 1000
No.2, 1000
No.3, 1000
No.4, 1000
No.5, 1000

请教高手，我的代码如何修改，才能达到我想要的结果？