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I have a util that takes an array and a predicate to perform a filtration of the array, however after using my custom type for the predicate I am getting an error stating

property 'name' does not exist on type 'T'

I thought that the generic property type T would have accepted anything?

Am I missing something obvious?

Array.ts

export type arrayPredicate = <T>(arg: T) => boolean;

ArrayUtil

static filterArray<T>(array: T[], arrayPred: arrayPredicate): T {
    const key =  Object.keys(array).find(obj => arrayPred(array[obj]));
    return array[key];
  }

Usage in test

const array = [
  {
    'name': 'object-1',
    'id': 1
  },
  {
    'name': 'object-2',
    'id': 2
  }
];

it(... , () => {

  // I get red squigglies under '.name'

  const myObj = ArrayUtils.filterArray(exceptionalStatuses, 
                                          (status => status.name === findStatus));

  ...

});

Of course, changing

I have a util that takes an array and a predicate to perform a filtration of the array, however after using my custom type for the predicate I am getting an error stating

property 'name' does not exist on type 'T'

I thought that the generic property type T would have accepted anything?

Am I missing something obvious?

Array.ts

export type arrayPredicate = <T>(arg: T) => boolean;

ArrayUtil

static filterArray<T>(array: T[], arrayPred: arrayPredicate): T {
    const key =  Object.keys(array).find(obj => arrayPred(array[obj]));
    return array[key];
  }

Usage in test

const array = [
  {
    'name': 'object-1',
    'id': 1
  },
  {
    'name': 'object-2',
    'id': 2
  }
];

it(... , () => {

  // I get red squigglies under '.name'

  const myObj = ArrayUtils.filterArray(exceptionalStatuses, 
                                          (status => status.name === findStatus));

  ...

});

Of course, changing

  • javascript
  • angular
  • typescript
  • types
Share Improve this question edited Oct 5, 2019 at 14:37 StepUp 38.3k16 gold badges92 silver badges157 bronze badges asked Oct 18, 2018 at 9:57 physicsboyphysicsboy 6,37822 gold badges77 silver badges139 bronze badges
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2 Answers 2

Reset to default 1

Change your arrayPredicate declaration as shown below.

export type arrayPredicate<T> = (arg: T) => boolean;

class ArrayUtils {
    static filterArray<T>(array: T[], arrayPred: arrayPredicate<T>): T {
    const key =  Object.keys(array).find(obj => arrayPred(array[obj]));
    return array[key];
  }
}

Since you are not declaring parameter in type for arrayPredicate, it is assumed to be empty object.

Here is working example,

TypeScript example

Need to add a type for your array for exmaple lets sat type of the array is SampleType[]. Then is should be

const array: SampleType[] = [
  {
    'name': 'object-1',
    'id': 1
  },
  {
    'name': 'object-2',
    'id': 2
  }
];

Then pass that type to the generic function

 ArrayUtils.filterArray<SampleType>(exceptionalStatuses, (status: SampleType => status.name === findStatus));

SampleType should be

export class SampleType{
  name: string,
  id: string
}

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