Undefined property of a typed Array (Typescript)?

Question

I've been struggling with a simple problem (but it's already givin' me a headache). I have the code below:

interface IFoo{
   ReturnFirstBarObject1(): string;
   FillBarArray(array: Array<Bar>): void;
}

class Bar {
  object1: string;
  object2: string;
}

class Foo implements IFoo{
  array: Array<Bar>;

  constructor(){
    this.array = new Array<Bar>();
  }

  public ReturnFirstBarObject1(): string {
     return this.array[0].object1;
  }

  public FillBarArray(array: Array<Bar>): void {
     this.array = array;
  }
}

$(document).ready(function(){
  var foo = new Foo();

  $.get('url/getBars?FooID=1')
   .done(function(data: any){
       foo.FillBarArray(data);
   });

  var object1 = foo.ReturnFirstBarObject1();
});

I don't know why but object1 returns for me as 'undefined' and when I highlight 'this.array[0]' it returns a JSon like this

"{'object1' : 'someString', 'object2' : 'someString'}"

I want to access object1 but it returns undefined and I can't do a workaround on the Json because typescript recognize the array object as a Bar.

Anyone knows why this is happening and what can I do to access Bar property properly ?

string object1 = ... is not valid syntax. Perhaps you meant let object1:string = ... ? Also, you instantiate Foo but never assign any values to array so array[0] would not exist. — Aaron Beall
– Aaron Beall, Commented May 16, 2016 at 0:41
Not sure what you are trying to achieve here, if you have a class Bar and you want to access its property you may directly use from the object of Bar with an string indexer like objOfBar['object1'] or objOfBar.object1 — Madhu Ranjan
– Madhu Ranjan, Commented May 16, 2016 at 0:46
@Aaron sorry, i'm already editing that. The values are provided by a return. The real problem is the value that return 'undefined' — João Pedro R. Carvalho
– João Pedro R. Carvalho, Commented May 16, 2016 at 0:49
I have an ajax that returns the values and insert them in the array. Everything runs smooth, with the exception of this that I can't access. — João Pedro R. Carvalho
– João Pedro R. Carvalho, Commented May 16, 2016 at 0:52
@MadhuRanjan I'm sorry if I expressed myself badly. My object is filled with an ajax return with an Array of Bars. The problem is that I don't know why the browser in runtime can't recognize the properties inside Bar. — João Pedro R. Carvalho
– João Pedro R. Carvalho, Commented May 16, 2016 at 1:01

Madhu Ranjan · Accepted Answer · 2020-08-31 18:15:48Z

1

It seems you are trying to get the first element before you have filled the array,

below code executes before your ajax calls fills the array, hence you are getting undefined error.

var object1 = foo.ReturnFirstBarObject1();

If you move this code inside ajax call it should work,

$.get('url/getBars?FooID=1')
  .done(function(data: Array<Bar>){
     foo.FillBarArray(data);
     var object1 = foo.ReturnFirstBarObject1();
});

edited Aug 31, 2020 at 18:15

answered May 16, 2016 at 1:16

Madhu Ranjan

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2 Comments

João Pedro R. Carvalho Over a year ago

@fips You got that, i'm feeling realy stupid now. My return in ajax was data: any, and it was binding the whole json to the array. I'll edit my question and you answer it and I'll give you a +1. thanks.

João Pedro R. Carvalho Over a year ago

@MadhuRanjan thanks for the help. My method where returning an Json and the binding didn't occur like I was thinking. Thanks guys, you're all awesome.

fips · Accepted Answer · 2016-05-16 01:55:44Z

0

The result here is a json string not a json object. Try $.getJSON.

Also @Madhu Ranjan's answer about jquery's callback possibly returning after the call to ReturnFirstBarObject1 is another thing to consider that could cause this problem.

answered May 16, 2016 at 1:55

fips

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