javascript - 为什么异常抛出后就不再认为发生了？

Question

在5.2 Algorithm Conventions ECMAScript® 语言规范 5.1 版:

If an algorithm is defined to “throw an exception”, execution of the algorithm is terminated and no result is returned. The calling algorithms are also terminated, until an algorithm step is reached that explicitly deals with the exception, using terminology such as “If an exception was thrown…”. Once such an algorithm step has been encountered the exception is no longer considered to have occurred.

为什么异常抛出后就不再认为发生了？我不明白。有一个算法步骤“处理”异常，所以我认为它应该被认为是“发生”的。

(想问之前先上网搜一下，但是不知道搜什么。)

Answer 1

可以用这个示例代码来解释:

// our algorithm
function foo()
{
    // throw the exception
    throw 'a ball';
    console.log('this is not output'); // terminated statement
}

// the calling algorithm
function bar()
{
    try {
        foo();
    } catch (e) {
        // dealing with the exception
    }
    // no longer an exception here
    console.log('all is fine');
}