I have successfully chained promises, but I find the way I did it enough complicated: I'm wondering if there is not a more elegant way to do it.
I use Angular2, Typescript and signalR.
I have a service getIntervention
that returns an object from the server by Id.
Before calling getIntervention
, I want to check the client to be connected to the server, and before connecting to the server, I want the SignalR scripts to be loaded.
So I created a first promise scriptLoadedPromise
that waits for the SignalR script to be loaded. When scriptLoadedPromise
is resolved a new promise connectionPromise
is created that waits for the connection to be established.
When connectionPromise
is resolved, call the service getIntervention
.
For each promise I added callbacks named scriptLoaded
and connectionDetected
that call resolve()
.
Here is my code:
public loadIntervention( numFI : number ) : Promise<Intervention>
{
let scriptLoadedPromise : Promise<Intervention> = new Promise( ( resolve, reject ) =>
{
// si le script est chargé alors la promesse est déjà tenue
if ( this.isScriptLoaded )
resolve();
else
this.scriptLoaded = ( () => { resolve(); } ) ;
}).then
( () => {
let connectionPromise : Promise<Intervention> = new Promise( (resolve, reject) =>
{
// si le serveur est connecté alors la promesse de connection est déjà tenue
if ( this.Connected )
resolve();
else
this.connectionDetected = ( () => { console.log("RECONNETED !!!!!"); resolve(); } );
} )
.then( () => { return this.proxy.server.getIntervention( numFI ); } );
return connectionPromise;
});
return scriptLoadedPromise;
}
Is there a way to simplify that implementation where 3 promises are chained ?
If these promises depend on each other, it's similar to what you created already. You could enhance the code-style of that, by putting the logic into separate methods like eg
private firstAction():Promise<any> {
return new Promise<any>(
(resolve, reject) => { ... }
);
}
private secondAction():Promise<any> {
return new Promise<any>(
(resolve, reject) => { ... }
);
}
execute() {
this.firstAction().then(
(firstResult:any) => this.secondAction().then(
(secondResult:any) => { ... }
);
)
}
If it's allowed that the promises are executed in parallel, you can make use of Promise.all()
, like eg
execute() {
let promises:Promise<any>[] = [];
promises.push(this.firstAction());
promises.push(this.secondAction());
Promise.all(promises).then(
() => { ... }
);
}
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