RxJs捕获错误并继续

Question

我有一个要解析的项目列表,但其中一个项目的解析可能会失败.

什么是"Rx-Way"来捕获错误但继续执行序列

代码示例:

var observable = Rx.Observable.from([0,1,2,3,4,5])
.map(
  function(value){
      if(value == 3){
        throw new Error("Value cannot be 3");
      }
    return value;
  });

observable.subscribe(
  function(value){
  console.log("onNext " + value);
  },
  function(error){
    console.log("Error: " + error.message);
  },
  function(){
    console.log("Completed!");
  });

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/4.0.6/rx.all.js"></script>

我想以非Rx方式做什么:

var items = [0,1,2,3,4,5];

for (var item in items){
  try{
    if(item == 3){
      throw new Error("Value cannot be 3");
    }
    console.log(item);
  }catch(error){
     console.log("Error: " + error.message);
  }
}

提前致谢

Answer 1

我建议你使用flatMap(现在mergeMap在rxjs版本5中),如果你不关心它们,它会让你崩溃错误.实际上,您将创建一个内部Observable,如果发生错误,可以吞下它.这种方法的优点是可以将运算符链接在一起,如果管道中的任何地方发生错误,它将自动转发到catch块.

const {from, iif, throwError, of, EMPTY} = rxjs;
const {map, flatMap, catchError} = rxjs.operators;

// A helper method to let us create arbitrary operators
const {pipe} = rxjs;

// Create an operator that will catch and squash errors
// This returns a function of the shape of Observable<T> => Observable<R>
const mapAndContinueOnError = pipe(
  //This will get skipped if upstream throws an error
  map(v => v * 2),
  catchError(err => {
    console.log("Caught Error, continuing")
    //Return an empty Observable which gets collapsed in the output
    return EMPTY;
  })
)

const observable = from([0, 1, 2, 3, 4, 5]).pipe(
  flatMap((value) => 
    iif(() => value != 3, 
      of(value), 
      throwError(new Error("Value cannot be 3"))
    ).pipe(mapAndContinueOnError)
  )
);

observable.subscribe(
  (value) => console.log("onNext " + value), (error) => console.log("Error: " + error.message), () => console.log("Completed!")
);

<script src="https://unpkg.com/rxjs/bundles/rxjs.umd.min.js"></script>

Answer 2

您需要切换到新的一次性流,如果在其中发生错误,将安全地处理,并保持原始流的活动:

Rx.Observable.from([0,1,2,3,4,5])
    .switchMap(value => {

        // This is the disposable stream!
        // Errors can safely occur in here without killing the original stream

        return Rx.Observable.of(value)
            .map(value => {
                if (value === 3) {
                    throw new Error('Value cannot be 3');
                }
                return value;
            })
            .catch(error => {
                // You can do some fancy stuff here with errors if you like
                // Below we are just returning the error object to the outer stream
                return Rx.Observable.of(error);
            });

    })
    .map(value => {
        if (value instanceof Error) {
            // Maybe do some error handling here
            return `Error: ${value.message}`;
        }
        return value;
    })
    .subscribe(
      (x => console.log('Success', x)),
      (x => console.log('Error', x)),
      (() => console.log('Complete'))
    );

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.4.1/Rx.min.js"></script>

有关此技术的更多信息,请参阅此博客文章:寻找肉丸:发生错误时继续使用RxJS Streams

Answer 3

为了使您endlessObservable$从垂死的，你可以把你failingObservable$在高阶绘图操作（例如switchMap，concatMap，exhaustMap...），并终止与内流吞下的错误empty()观察到没有返回值。

使用 RxJS 6：

endlessObservable$
    .pipe(
        switchMap(() => failingObservable$
            .pipe(
                catchError((err) => {
                    console.error(err);
                    return EMPTY;
                })
            )
        )
    );

Answer 4

实际上，您可以在映射函数中使用try/catch来处理错误。这是代码片段

var source = Rx.Observable.from([0, 1, 2, 3, 4, 5])
    .map(
        function(value) {
            try {
                if (value === 3) {
                    throw new Error("Value cannot be 3");
                }
                return value;

            } catch (error) {
                console.log('I caught an error');
                return undefined;
            }
        })
    .filter(function(x) {
        return x !== undefined; });


source.subscribe(
    function(value) {
        console.log("onNext " + value);
    },
    function(error) {
        console.log("Error: " + error.message);
    },
    function() {
        console.log("Completed!");
    });

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/4.0.6/rx.all.js"></script>