Angular 5 RxJs concatMap,switchMap,mergeMap哪个? [英] Angular 5 RxJs concatMap,switchMap,mergeMap which?
问题描述
我有此方法可通过localstorage获取令牌,如果令牌不存在或已过期,我将调用API以获取另一个令牌并将其存储到localstorage.
I have this method to get token via localstorage, if token is not exist or is expired, I will call API to get another token and store to localstorage.
在这种情况下,我应该使用哪个地图,当前是否使用mergeMap或其他方式?
In this case, which map should I use, currently using mergeMap, or other way to do this?
public doGetToken():Observable<Token> {
return this.loadToken().pipe( //get via localstorage
map(token=>{
let valid = this.validateTokenIsValid(token);
let data = {
token: token,
valid: valid
};
return data;
}),
mergeMap(data=>{
if (!data.valid) {
return this.doApiGetToken(data.token).pipe(
map(
token=>{
this.saveToken(token); //save to localstorage
return token;
}
)
);
} else {
return of(data.token);
}
})
);
版本:Angular 5,rxjs5
version: Angular 5, rxjs5
谢谢.
推荐答案
如果您仅提出一个请求,则没关系使用哪种地图.
If you only make one request, then it doesn't matter which map you use.
mergeMap(也称为flatMap),concatMap,exhaustMap或switchMap的行为相同.
mergeMap (also called flatMap), concatMap , exhaustMap or switchMap will behave the same.
当您发出多个值时,这些运算符的行为会有所不同:
These operators behave differently when you emit more than 1 value:
switchMap
会将映射应用于收到的最新输入
will apply the mapping to the latest input received:
Src : -----A----B----C--D-E-------
switchMap (x => x--x) // emit x twice when received
Out: ------A--A-B--B-C-D-E--E----
concatMap
将在完成另一个输入之前完成映射:
will finish the mapping before taking another input:
Src : -----A----B----C--D-E-----------
concatMap (x => x--x) // emit x twice when received
Out: ------A--A-B--B-C--C--D--D-E--E
合并地图
类似于concatMap,但是它不等待映射完成.结果可能会重叠:
is like concatMap, but it doesn't wait for mapping to complete. The results can overlap though:
Src : -----A----B----C-D---E-----------
mergeMap (x => x--x) // emit x twice when received
Out: ------A--A-B--B-C-D-C-D-E--E-----
排气图
就像一个反向的switchMap,它为输出赋予优先级:
is like a reversed switchMap, it gives priority to the output:
Src : -----A--------B----C-D---E-----------
exhaustMap (x => x--x--x) // emit x thrice when received
Out: ------A--A--A--B--B--B-D--D--D-------
有关更多信息:
https://medium.com/@ vdsabev/the-simple-difference-between-rxjs-switchmap-and-mergemap-397c311552a5
大理石图:
http://rxmarbles.com/#mergeMap
我将代码的简化移到底部,以使一般信息一目了然.
Edit : I moved the simplification of your code to the bottom to make the general information visible at first sight.
public doGetToken(): Observable<Token> {
return this.loadToken()
.pipe( //get via localstorage
mergeMap(token => {
if(!this.validateTokenIsValid(token))
return of(token)
return this.doApiGetToken(token)
.pipe(
tap( token => this.saveToken(token)) //save to localstorage
);
})
)
};
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