Javascript 承诺：then vs then + catch
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Promise : then vs then + catch
提问by Magus
Is there any difference between the 2 followings codes ?
以下2个代码之间有什么区别吗？
myPromise.then(function() {
console.log('success');
}).catch(function() {
console.log('error');
});
myPromise.then(function() {
console.log('success');
}, function() {
console.log('error');
});
I know thenand catchreturns new promises resolved or rejected with the value returns in the callback. But i see the 2 codes around the web and i'm curious about the real differences between the 2 codes.
我知道then并catch返回已解决或拒绝的新承诺，并在回调中返回值。但是我在网上看到了 2 个代码，我很好奇这 2 个代码之间的真正区别。
回答by fuyushimoya
In your current code, they act the same because console.log('success');will not fail.
在您当前的代码中，它们的行为相同，因为console.log('success');不会失败。
However, if you write something like this...
但是，如果你写这样的东西......
myPromise.then(function() {
// Some error may happen
throw('An exception that would be caught');
}).catch(function() {
console.log('error');
});
// Is the same as this, the errHandle tries to catch any unhandled error
// from previous result.
myPromise.then(func, null).then(null, errHandle);
myPromise.then(function() {
// Some error may happen
throw('An unhandled exception.');
}, function() {
// This won't log the error if it happens in the
// some error may happen block.
console.log('error');
});
// Is the same as this, the errHandle will handle errors from previous result,
// but it won't handle errs in func.
myPromise.then(func, errHandle)
The second form can't catch that error, while the first can.
第二种形式不能捕捉到那个错误，而第一种可以。
Snippet for test:
测试片段：
// An function that may error and throw exception.
function funcThatThrows(test) {
throw(`oops - error in test ${test}`);
}
function errHandler(exception) {
console.log('We got an exception: ', exception);
}
// Expect: We got an exception: oops - error in test 1
Promise.resolve(1).then(funcThatThrows).catch(errHandler);
// Is the same as below, the errHandler tries to catch any unhandled error
// from previous result.
// Expect: We got an exception: oops - error in test 2
Promise.resolve(2).then(funcThatThrows, null).then(null, errHandler);
// If put the function and handler in the same then, the exception won't be caught.
// Expect: Uncaught (in promise) oops - error in test 3
Promise.resolve(3).then(funcThatThrows, errHandler);回答by jkris
I'm guessing it depends on how the Promise is implemented. As far as I know jQuery implements it in a different fashion.
我猜这取决于 Promise 的实现方式。据我所知 jQuery 以不同的方式实现它。
The second you gave seems to be the jQuery version.
您提供的第二个似乎是 jQuery 版本。
