承诺：那么vs那么+抓住[重复]

Question

这个问题在这里已有答案：

• When is .then(success, fail) considered an antipattern for promises? 6个答案

以下2个代码有什么区别吗？

myPromise.then(function() {
    console.log('success');
}).catch(function() {
    console.log('error');
});

myPromise.then(function() {
    console.log('success');
}, function() {
    console.log('error');
});

我知道then和catch返回新的承诺已被解决或拒绝回调中的值返回。但我看到网络上的2个代码，我很好奇2代码之间的真正差异。

Answer 1

在您当前的代码中，它们的行为相同，因为console.log('success');不会失败。

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)

第二种形式无法捕获该错误，而第一种形式则无法捕获。

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);

Answer 2

我猜它取决于Promise的实现方式。据我所知，jQuery在different fashion中实现它。

你给的第二个似乎是jQuery版本。