javascript - 由于 "a+?"是惰性的，为什么 "a+?b"匹配 "aaab"？

Question

在使用 JavaScript:权威指南 学习 javascript 中的正则表达式时，我对这段话感到困惑:

But /a+?/ matches one or more occurrences of the letter a, matching as few characters as necessary. When applied to the same string, this pattern matches only the first letter a.

…

Now let’s use the nongreedy version: /a+?b/. This should match the letter b preceded by the fewest number of a’s possible. When applied to the same string “aaab”, you might expect it to match only one a and the last letter b. In fact, however, this pattern matches the entire string, just like the greedy version of the pattern.

为什么会这样？

这是书中的解释:

This is because regular-expression pattern matching is done by finding the first position in the string at which a match is possible. Since a match is possible starting at the first character of the string,shorter matches starting at subsequent characters are never even considered.

我不明白。谁能给我更详细的解释？

Answer 1

好的，现在您有了搜索空间“aaabc”和模式/a+?b/

/a+?b/匹配“a”吗？没有。

/a+?b/匹配“aa”吗？没有。

/a+?b/匹配“aaa”吗？没有。

/a+?b/是否匹配“aaab”？是的。