关于javascript：承诺：那么vs那么+ catch

Promise : then vs then + catch

本问题已经有最佳答案，请猛点这里访问。

以下2个代码有什么区别吗？

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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返回已在回调中使用值返回解析或拒绝的新promise。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。

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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......

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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：

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// 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);