【JS】try...catch

[Rocco]

注意

catch 内一定要加 console.error(error)，不然 try 块里出现 BUG 时你会想哭的

示例代码：

try {
...
} catch (error) {
  console.error(error)
}

谁加谁知道，加了都说好

类似的还有 Promise，Promise 里的函数是被 try...catch 包裹着的

return in finally override try

function example() {
  try {
    return true;
  } finally {
    return false;
  }
}

example(); // false

According to ECMA-262 (5ed, December 2009), in pp. 96:

The production TryStatement : try Block Finally is evaluated as follows:

Let B be the result of evaluating Block.
Let F be the result of evaluating Finally.
If F.type is normal, return B.
Return F.

And from pp. 36:

The Completion type is used to explain the behaviour of statements (break, continue, return and throw) that perform nonlocal transfers of control. Values of the Completion type are triples of the form (type, value, target), where type is one of normal, break, continue, return, or throw, value is any ECMAScript language value or empty, and target is any ECMAScript identifier or empty.

It's clear that return false would set completion type of finally as return, which cause try ... finally to do 4. Return F.

参考

• https://stackoverflow.com/questions/3837994/why-does-a-return-in-finally-override-try/3838130#3838130