javascript - V8 会自动缓存编译后的正则表达式吗？

Question

所以我知道在 Javascript 中实例化正则表达式会导致它自动编译，如果该正则表达式存储在变量中，它将被重用而无需重新编译。示例:

var re = /[Ff]oo|[Bb]ar/;
"Foo".match(re); // ["Foo"]
"Baz".match(re); // null

但是，重复的正则表达式是否会重新编译，或者 V8 (Chrome/Node.js) 是否会智能地重用它们(就像 PHP 对 preg_* 函数所做的那样)？

function isFooBar(str) {
  return str.match(/[Ff]oo|[Bb]ar/);
}
isFooBar("Foo"); // ["Foo"]
isFooBar("Baz"); // null

为了澄清，我知道第一个示例会导致正则表达式的一次编译。但是第二个例子呢？

Answer 1

好吧，让我们找出答案。

// http://stackoverflow.com/questions/3466850/complex-password-regular-expression
function isFooBar(str) {
  return 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}
console.time('1');isFooBar("Foo");console.timeEnd('1');
console.time('2');isFooBar("Bar");console.timeEnd('2');

(打开控制台并运行上面的代码片段，看看结果是否适合您的浏览器。)

在 Node.js 0.10.36 (V8 3.14.5.9) 上:

1: 65ms
2: 0ms

在 io.js 1.6.3 (V8 4.1.0.27) 上:

1: 32ms
2: 0ms

所以，我想你问题的答案是是，V8 能够自动缓存正则表达式。

<小时/>

编辑:

尽管 V8能够进行此类优化，但实际上它可能不会选择始终使用此优化。 V8 针对不同情况有许多复杂的启发式方法，例如何时内联函数、何时优化函数、何时取消优化函数等。除非您是 V8 开发人员，否则许多启发式方法会显得奇怪或意外或两者兼而有之。

我自己不是 V8 开发人员，我不知 Prop 体问题的答案，也不知道正则表达式是否总是自动缓存。然而，即使我知道答案， future 也可能会改变。因此，当您编写代码时，我仍然建议以明确该变量的意图的方式存储正则表达式。对于上面的示例，这意味着将正则表达式变量取出函数isFooBar()。

另一个问题是这个正则表达式是如何创建的。上面的例子和OP的问题是用 regular expression literal 声明的。 。但是，如果您使用 new RegExp() constructor ，V8 不允许缓存正则表达式，因为它可能在运行时发生变化。