Question

我有以下JavaScript（Typescript）示例，其中我初始化一个数组，然后推送每小时的时间戳，直到该范围中包含end时间戳。

let res = [start];
while (res[res.length - 1].isBefore(end)) {
    let nextTime = res[res.length - 1].add(1, 'hour'); // add one hour to the previous result - this is a moment.js instance
    console.log('loop', nextTime.format())
    res.push(nextTime);
}
res.forEach(val => console.log('result', val.format()))

循环中的console.log会记录预期值，例如

循环2017-03-27T18：00：00 + 01:00

循环2017-03-27T19：00：00 + 01:00

循环2017-03-27T20：00：00 + 01:00

但是，结果数组似乎只包含正确数量的记录，但它们都是最终值，例如

结果2017-03-28T18：00：00 + 01:00

结果2017-03-28T18：00：00 + 01:00

为什么会这样？

Answer 1

MomentJS对象是具有状态的可变（可更改）对象。在MomentJS对象上调用add会修改它，但不会创建新对象;它只返回对同一对象的引用。所以说你从这开始：

     +−−−−−−−−−+        
res−>| (array) |        
     +−−−−−−−−−+        +−−−−−−−−−−+    
     | 0       |−−−−−−−>| (object) |    
     +−−−−−−−−−+        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                        | d:       |−−>|                  (Date)                  | 
                        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                                       | [[TimeValue]]: 2017−03−27T18:00:00+01:00 |
                                       +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+

你的

let nextTime = moment(res[res.length - 1]).add(1, 'hour');
// ...
res.push(nextTime);

修改该对象并将其另一个引用推送到res：

     +−−−−−−−−−+        
res−>| (array) |        
     +−−−−−−−−−+        +−−−−−−−−−−+   
     | 0       |−−−−+−−>| (object) |   
     | 1       |−−−/    +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+
     +−−−−−−−−−+        | d:       |−−>|                  (Date)                  |
                        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+
                                       | [[TimeValue]]: 2017−03−27T19:00:00+01:00 |
                                       +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+

注意对象的状态（MomentJS对象使用的Date中的[[TimeValue]]如何变化。

如果再次执行此操作，我们只需再次更新：

     +−−−−−−−−−+        
res−>| (array) |        
     +−−−−−−−−−+        +−−−−−−−−−−+   
     | 0       |−−−−+−−>| (object) |   
     | 1       |−−−/    +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+
     | 2       |−−/     | d:       |−−>|                  (Date)                  |
     +−−−−−−−−−+        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+
                                       | [[TimeValue]]: 2017−03−27T20:00:00+01:00 |
                                       +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+

相反，您想要创建一个新对象。你可以用moment克隆原文来做到这一点。

let nextTime = moment(res[res.length - 1]).add(1, 'hour');
// ------------^^^^^^^   ----------------^
// ...
res.push(nextTime);

如果你这样做，那么从同一个起点，我们得到：

     +−−−−−−−−−+        
res−>| (array) |        
     +−−−−−−−−−+        +−−−−−−−−−−+   
     | 0       |−−−−−−−>| (object) |   
     | 1       |−−−−+   +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+
     | 2       |−−+ |   | d:       |−−>|                  (Date)                  |
     +−−−−−−−−−+  | |   +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                  | |                  | [[TimeValue]]: 2017−03−27T18:00:00+01:00 | 
                  | |   +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                  | +−−>| (object) |                                                
                  |     +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                  |     | d:       |−−>|                  (Date)                  |
                  |     +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                  +−−−−>               | [[TimeValue]]: 2017−03−27T19:00:00+01:00 | 
                        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                        | (object) |                                                
                        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
                        | d:       |−−>|                  (Date)                  |
                        +−−−−−−−−−−+   +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+
                                       | [[TimeValue]]: 2017−03−27T20:00:00+01:00 |
                                       +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+

array.push（）仅包含循环的最终值

1 个答案: