What happens when a typed Array in Typescript has an undefined property?

I've encountered an issue with a seemingly simple problem that's causing me quite the headache. The code snippet in question is provided 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();
});

Upon testing, I noticed that when attempting to access 'object1', it returns as 'undefined'. Furthermore, highlighting 'this.array[0]' reveals a JSON string like so:

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

My objective is to properly access the object1 property, but due to TypeScript recognizing the array object as a Bar, I am unable to find a workaround.

If anyone has insights into why this behavior is occurring and suggestions on how I can correctly access the Bar property, your input would be greatly appreciated!

Answer №1

Looks like you're attempting to access the first element of an array before it's been filled,

The code below is running before your ajax calls populate the array, hence the undefined error.

var object1 = foo.ReturnFirstBarObject1();

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

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

Answer №2

This output is in the format of a JSON string, not a JSON object. You may want to consider using $.getJSON for parsing it.

In addition, @Madhu Ranjan's suggestion regarding jQuery's callback possibly executing after the ReturnFirstBarObject1 function call is another potential factor contributing to this issue.

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