Question

注意：我在现实生产应用程序中遇到了这个问题。虽然我能够解决它，但遗憾的是，我不明白为什么它的表现如此。

我有这个正则表达式

// Notice global modified at the end.
const regexExp = /(\d{4})-(\d{2})-(\d{2})T((\d{2}):(\d{2}):(\d{2}))\.(\d{3})Z/g;

// Array of same string 6 times.
[
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
]
.forEach((i) => console.log(regexExp.test(i)));

    // This would print
    // true
    // true
    // false -> Why?
    // true
    // true
    // false -> why?

您可以点击Run Code snippet来运行代码。令我感到困惑的是，为什么每false时间都会测试3rd？

以下两种解决方案往往有效。

Defining the Expression inside the forEach block.

// Array of same string 6 times.
[
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
]
.forEach((i) => {
  const regexExp = /(\d{4})-(\d{2})-(\d{2})T((\d{2}):(\d{2}):(\d{2}))\.(\d{3})Z/g;
  console.log(regexExp.test(i))
});

    // This would print
    // true
    // true
    // true -> Yay!!
    // true
    // true
    // true -> Yay!!

我知道为什么会这样，因为基本上每个块范围都会创建新的正则表达式。即对于每个循环，创建一个新的正则表达式，因此相同的对象永远不会用于第二次调用。

方法2：Use i modifier instead of g modified

// Notice global modified at the end.
const regexExp = /(\d{4})-(\d{2})-(\d{2})T((\d{2}):(\d{2}):(\d{2}))\.(\d{3})Z/i;

// Array of same string 6 times.
[
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
  '{"ApplicationDate.Time.DateTime":{"$gte":"2017-08-14T11:27:26.034Z","$lt":"2017-08-24T11:27:26.034Z"}}',
]
.forEach((i) => console.log(regexExp.test(i)));

    // This would print
    // true
    // true
    // true -> Yay!!
    // true
    // true
    // true -> Yay!!

为什么会发生这种情况，

为什么方法2有效？
当我使用i修饰符时，为什么它有效？为什么它不适用于g修饰符？
为什么每次3rd测试？为什么不4th或5th或any random测试？

似乎在使用g修饰符改变RegExp实例时，为什么会这样？

如果有人能对这个问题有所了解，我真的很感激。

提前致谢。

有人可以解释为什么RegExp.test会以这种方式表现吗？

0 个答案: