打字稿：箭头功能-TS2339：类型“ {}”上不存在属性

Question

Using Angular, I often get typescript compile errors when using fat arrow functions inside an rxjs stream.

I can still run the app and it does transpile, but I would like to know how to get rid of the error and understand it.

Given:

this.data$ = this.route.params
        .switchMap(params =>  
             Observable.forkJoin([
                 Observable.of(params),
                 this.http.get('/api', { param1: params.param1, param2: params.param2 })
        ])
        //**Errors from this part below**
        .map(([params, data]) => data.prop1 + ' - ' + params.param1)

I get the errors:

ERROR in [at-loader] file.ts:xx:xx TS2339: Property 'prop1' does not exist on type '{}'.

ERROR in [at-loader] file.ts:xx:xx TS2339: Property 'param1' does not exist on type '{}'.

Why does it complain about this?

Answer 1

Try this one:

this.data$ = this.route.params
    .switchMap((params: any) =>  
         Observable.forkJoin([
             Observable.of(params),
             this.http.get('/api', { param1: params.param1, param2: params.param2 })
    ])
    //**Errors from this part below**
    .map(([params, data]: [any, any]) => data.prop1 + ' - ' + params.param1)