Getting “Cannot read property 'http' of undefined” with Angular 7












2














I'm working on an Angular 7 project, and I'm facing a weird problem that took me some considerable time to identify, but I don't know why this is happening and I hope you guys can help me. I created a service using angular-cli, and then I implemented it as follows:





import {Injectable} from '@angular/core';
import {HttpClient} from "@angular/common/http";
import {forkJoin, Observable} from "rxjs";
import {map} from "rxjs/operators";

@Injectable({
providedIn: 'root'
})
export class SampleService {

constructor(private http: HttpClient) {
}

save(sample: Sample): Observable {
return this.http.post("http://localhost:3000/samples", sample).pipe(map(this.parser));
}

saveAll(samples: Sample): Observable {
return forkJoin(samples.map(this.save))
}

private parser = (value): Sample => new Sample(value.name);
}

export class Sample {
name: string;

constructor(name: string) {
this.name = name;
}
}



I put a breakpoint on each method. When I run it I get the following:



First breakpoint stop



As you can see, everything seems ok in the first breakpoint, so let's go to the next.



Second breakpoint stop



Now everything is undefined, and I get the following error in the console:





ERROR TypeError: Cannot read property 'http' of undefined



If I change this line:





forkJoin(samples.map(this.save))



to





forkJoin(samples.map(sample => this.save(sample)))



When I rerun the code. I get:



Third breakpoint stop



And now everything seems to be ok, and the code works just fine. As a java developer, in a similar situation, the first way is comparable to a method reference and it would work just fine, why in TypeScript it doesn't?










share|improve this question


















  • 1




    this is how javascript works. If you want to keep the first option then write it as instance function github.com/Microsoft/TypeScript/wiki/…
    – yurzui
    Dec 27 '18 at 19:53






  • 1




    Its related to the context of object. In first case context will change however in second option context will always be the same. Refer- ryanmorr.com/understanding-scope-and-context-in-javascript
    – Sunil Singh
    Dec 27 '18 at 20:00










  • Possible duplicate of How to access the correct `this` inside a callback?
    – JB Nizet
    Dec 27 '18 at 20:10










  • return forkJoin(samples.map(sample => this.save(sample)));
    – JB Nizet
    Dec 27 '18 at 20:11
















2














I'm working on an Angular 7 project, and I'm facing a weird problem that took me some considerable time to identify, but I don't know why this is happening and I hope you guys can help me. I created a service using angular-cli, and then I implemented it as follows:





import {Injectable} from '@angular/core';
import {HttpClient} from "@angular/common/http";
import {forkJoin, Observable} from "rxjs";
import {map} from "rxjs/operators";

@Injectable({
providedIn: 'root'
})
export class SampleService {

constructor(private http: HttpClient) {
}

save(sample: Sample): Observable {
return this.http.post("http://localhost:3000/samples", sample).pipe(map(this.parser));
}

saveAll(samples: Sample): Observable {
return forkJoin(samples.map(this.save))
}

private parser = (value): Sample => new Sample(value.name);
}

export class Sample {
name: string;

constructor(name: string) {
this.name = name;
}
}



I put a breakpoint on each method. When I run it I get the following:



First breakpoint stop



As you can see, everything seems ok in the first breakpoint, so let's go to the next.



Second breakpoint stop



Now everything is undefined, and I get the following error in the console:





ERROR TypeError: Cannot read property 'http' of undefined



If I change this line:





forkJoin(samples.map(this.save))



to





forkJoin(samples.map(sample => this.save(sample)))



When I rerun the code. I get:



Third breakpoint stop



And now everything seems to be ok, and the code works just fine. As a java developer, in a similar situation, the first way is comparable to a method reference and it would work just fine, why in TypeScript it doesn't?










share|improve this question


















  • 1




    this is how javascript works. If you want to keep the first option then write it as instance function github.com/Microsoft/TypeScript/wiki/…
    – yurzui
    Dec 27 '18 at 19:53






  • 1




    Its related to the context of object. In first case context will change however in second option context will always be the same. Refer- ryanmorr.com/understanding-scope-and-context-in-javascript
    – Sunil Singh
    Dec 27 '18 at 20:00










  • Possible duplicate of How to access the correct `this` inside a callback?
    – JB Nizet
    Dec 27 '18 at 20:10










  • return forkJoin(samples.map(sample => this.save(sample)));
    – JB Nizet
    Dec 27 '18 at 20:11














2












2








2







I'm working on an Angular 7 project, and I'm facing a weird problem that took me some considerable time to identify, but I don't know why this is happening and I hope you guys can help me. I created a service using angular-cli, and then I implemented it as follows:





import {Injectable} from '@angular/core';
import {HttpClient} from "@angular/common/http";
import {forkJoin, Observable} from "rxjs";
import {map} from "rxjs/operators";

@Injectable({
providedIn: 'root'
})
export class SampleService {

constructor(private http: HttpClient) {
}

save(sample: Sample): Observable {
return this.http.post("http://localhost:3000/samples", sample).pipe(map(this.parser));
}

saveAll(samples: Sample): Observable {
return forkJoin(samples.map(this.save))
}

private parser = (value): Sample => new Sample(value.name);
}

export class Sample {
name: string;

constructor(name: string) {
this.name = name;
}
}



I put a breakpoint on each method. When I run it I get the following:



First breakpoint stop



As you can see, everything seems ok in the first breakpoint, so let's go to the next.



Second breakpoint stop



Now everything is undefined, and I get the following error in the console:





ERROR TypeError: Cannot read property 'http' of undefined



If I change this line:





forkJoin(samples.map(this.save))



to





forkJoin(samples.map(sample => this.save(sample)))



When I rerun the code. I get:



Third breakpoint stop



And now everything seems to be ok, and the code works just fine. As a java developer, in a similar situation, the first way is comparable to a method reference and it would work just fine, why in TypeScript it doesn't?










share|improve this question













I'm working on an Angular 7 project, and I'm facing a weird problem that took me some considerable time to identify, but I don't know why this is happening and I hope you guys can help me. I created a service using angular-cli, and then I implemented it as follows:





import {Injectable} from '@angular/core';
import {HttpClient} from "@angular/common/http";
import {forkJoin, Observable} from "rxjs";
import {map} from "rxjs/operators";

@Injectable({
providedIn: 'root'
})
export class SampleService {

constructor(private http: HttpClient) {
}

save(sample: Sample): Observable {
return this.http.post("http://localhost:3000/samples", sample).pipe(map(this.parser));
}

saveAll(samples: Sample): Observable {
return forkJoin(samples.map(this.save))
}

private parser = (value): Sample => new Sample(value.name);
}

export class Sample {
name: string;

constructor(name: string) {
this.name = name;
}
}



I put a breakpoint on each method. When I run it I get the following:



First breakpoint stop



As you can see, everything seems ok in the first breakpoint, so let's go to the next.



Second breakpoint stop



Now everything is undefined, and I get the following error in the console:





ERROR TypeError: Cannot read property 'http' of undefined



If I change this line:





forkJoin(samples.map(this.save))



to





forkJoin(samples.map(sample => this.save(sample)))



When I rerun the code. I get:



Third breakpoint stop



And now everything seems to be ok, and the code works just fine. As a java developer, in a similar situation, the first way is comparable to a method reference and it would work just fine, why in TypeScript it doesn't?







angular typescript rxjs






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share|improve this question











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asked Dec 27 '18 at 19:49









Felipe Belluco

73069




73069








  • 1




    this is how javascript works. If you want to keep the first option then write it as instance function github.com/Microsoft/TypeScript/wiki/…
    – yurzui
    Dec 27 '18 at 19:53






  • 1




    Its related to the context of object. In first case context will change however in second option context will always be the same. Refer- ryanmorr.com/understanding-scope-and-context-in-javascript
    – Sunil Singh
    Dec 27 '18 at 20:00










  • Possible duplicate of How to access the correct `this` inside a callback?
    – JB Nizet
    Dec 27 '18 at 20:10










  • return forkJoin(samples.map(sample => this.save(sample)));
    – JB Nizet
    Dec 27 '18 at 20:11














  • 1




    this is how javascript works. If you want to keep the first option then write it as instance function github.com/Microsoft/TypeScript/wiki/…
    – yurzui
    Dec 27 '18 at 19:53






  • 1




    Its related to the context of object. In first case context will change however in second option context will always be the same. Refer- ryanmorr.com/understanding-scope-and-context-in-javascript
    – Sunil Singh
    Dec 27 '18 at 20:00










  • Possible duplicate of How to access the correct `this` inside a callback?
    – JB Nizet
    Dec 27 '18 at 20:10










  • return forkJoin(samples.map(sample => this.save(sample)));
    – JB Nizet
    Dec 27 '18 at 20:11








1




1




this is how javascript works. If you want to keep the first option then write it as instance function github.com/Microsoft/TypeScript/wiki/…
– yurzui
Dec 27 '18 at 19:53




this is how javascript works. If you want to keep the first option then write it as instance function github.com/Microsoft/TypeScript/wiki/…
– yurzui
Dec 27 '18 at 19:53




1




1




Its related to the context of object. In first case context will change however in second option context will always be the same. Refer- ryanmorr.com/understanding-scope-and-context-in-javascript
– Sunil Singh
Dec 27 '18 at 20:00




Its related to the context of object. In first case context will change however in second option context will always be the same. Refer- ryanmorr.com/understanding-scope-and-context-in-javascript
– Sunil Singh
Dec 27 '18 at 20:00












Possible duplicate of How to access the correct `this` inside a callback?
– JB Nizet
Dec 27 '18 at 20:10




Possible duplicate of How to access the correct `this` inside a callback?
– JB Nizet
Dec 27 '18 at 20:10












return forkJoin(samples.map(sample => this.save(sample)));
– JB Nizet
Dec 27 '18 at 20:11




return forkJoin(samples.map(sample => this.save(sample)));
– JB Nizet
Dec 27 '18 at 20:11












1 Answer
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oldest

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1














this is contextual. Every function defined using function definition gets its own this.
Arrow function definition works differently in that, it binds the parent context to the function body, making this refer to the parent this. It is similar to defining a function and binding it explicitly like:



function(doc){
//function body
}).bind(this)





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    1 Answer
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    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1














    this is contextual. Every function defined using function definition gets its own this.
    Arrow function definition works differently in that, it binds the parent context to the function body, making this refer to the parent this. It is similar to defining a function and binding it explicitly like:



    function(doc){
    //function body
    }).bind(this)





    share|improve this answer


























      1














      this is contextual. Every function defined using function definition gets its own this.
      Arrow function definition works differently in that, it binds the parent context to the function body, making this refer to the parent this. It is similar to defining a function and binding it explicitly like:



      function(doc){
      //function body
      }).bind(this)





      share|improve this answer
























        1












        1








        1






        this is contextual. Every function defined using function definition gets its own this.
        Arrow function definition works differently in that, it binds the parent context to the function body, making this refer to the parent this. It is similar to defining a function and binding it explicitly like:



        function(doc){
        //function body
        }).bind(this)





        share|improve this answer












        this is contextual. Every function defined using function definition gets its own this.
        Arrow function definition works differently in that, it binds the parent context to the function body, making this refer to the parent this. It is similar to defining a function and binding it explicitly like:



        function(doc){
        //function body
        }).bind(this)






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Dec 27 '18 at 20:42









        Aragorn

        1,95011226




        1,95011226






























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