How to convert this array element in a string in typescript?

Question

I have this array called fieldlist which is coming from the below http.get request in angular 2 component. I have declared it like this .

                   fieldlist: string[] = [];

then I assigned its value using iteration of json resposne.

               this.http.get(getform_endpoint,requestOptions).map((res: 
                                        Response) => res.json()).subscribe(
                          res => { 

                   this.FormData = res.schema;


                     res.fields.forEach(element => {
                         this.fieldlist.push(element);
                     });


          });

Now in another function like this

         create_hidden_qp() {


            let elementsnamevalue = this.fieldlist.join();
            console.log("hello", this.fieldlist.join());

      }

when I convert it to string using this lines it gives me blank "" response

but when I print it like this

                 console.log("hello", this.fieldlist);

I am able to see the perfect array like this.

           hello[] 0 :"userroleid" 1: "ruletype" 2: "employeeid"

So what I am missing?

A) wrong declaration? b) wrong assigment? c) wrong access to array elements?

I have tried this.fieldlist[0], this.fieldlist[1] etc, but its undefined. I have tried this.fieldlist.tostring() but its also gives me blank response. What I am missing? — Talk is Cheap Show me Code
– Talk is Cheap Show me Code, Commented Jan 22, 2018 at 15:17
option d), wrong timing. You probably try to access the fieldlist before the response has completed. Remember that JavaScript, and with it TypeScript are async languages — Poul Kruijt
– Poul Kruijt, Commented Jan 22, 2018 at 15:20
The join function needs an argument to join an array. Try using something like join(' ') — user4676340
– user4676340, Commented Jan 22, 2018 at 15:21
@PierreDuc Yup that may be a new case but then why I am able to read when printing it raw like this? console.log("hello", this.fieldlist); — Talk is Cheap Show me Code
– Talk is Cheap Show me Code, Commented Jan 22, 2018 at 15:21
@Jaydeep because the console holds a reference and will actually update when the data does come through — BradleyDotNET
– BradleyDotNET, Commented Jan 22, 2018 at 15:24

Poul Kruijt · Accepted Answer · 2018-01-22 15:50:15Z

1

You should call the create_hidden_qp after your request has finished:

this.http.get(getform_endpoint,requestOptions).map(r => r.json()).subscribe(res => { 
  this.FormData = res.schema;

  res.fields.forEach(element => {
    this.fieldlist.push(element);
  });

  this.create_hidden_qp();
});

answered Jan 22, 2018 at 15:50

Poul Kruijt

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4 Comments

Talk is Cheap Show me Code Over a year ago

This has make sure that I got the value when needed. Amazing answer. Thank you all.

Talk is Cheap Show me Code Over a year ago

But I am still curios to know that why after USING .join I am not able to get value but when I print it as raw, got it. Is it because I just passed by value to console as opposed to passing by reference when I am able to see it.

Poul Kruijt Over a year ago

@Jaydeep Yes, that's a thing of the console, you just log a reference, and once you actually open the array in the console, your request has already finished, and it will show the filled array :)

Talk is Cheap Show me Code Over a year ago

Ok so lesson learned is while using async language, Don't delay assignment and conversion as it my defer.

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