javascript - 似乎 JavaScript RegExp 没有找到 "leftmost longest"

Question

我观察到这些结果:

// Test 1:
var re = /a|ab/;
"ab".match(re); // returns ["a"]   <--- Unexpected

// Test 2:
re = /ab|a/;
"ab".match(re); // returns ["ab"]

由于“最左边最长”的原则，我希望测试 1 和 2 都返回 ["ab"]。我不明白为什么正则表达式中两个备选方案的顺序会改变结果。

Answer 1

在下面找到原因:

Note that alternatives are considered left to right until a match is found. If the left alternative matches, the right alternative is ignored, even if it would have produced a “better” match. Thus, when the pattern /a|ab/ is applied to the string “ab,” it matches only the first letter.

(来源:Oreilly - Javascript Pocket Reference - 第 9 章正则表达式)

谢谢。