TS2461: Type 'T' is not an array type-CodePudding

So I have a generic function, where argument array can be either of type Alfa[] or Beta[].

export interface Alfa {
  id: number;
  name: string;
  propertyOne: string
  propertyTwo: string
  creation_date: string;
  updation_date: string;
}

export interface Beta {
  id: number;
  propertyThree: string;
  propetryFour: boolean;
  creation_date: string;
  updation_date: string;
}

import { isNil } from "lodash";

export const sort= <T>(array?: T | null) => {
  if (isNil(array)) return;
  return [...array].sort((a, b) => {
    return Date.parse(b.creation_date) - Date.parse(a.creation_date);
  });
};

So in if (isNil(array)) return; I exclude null | undef, and when function iterates through array , I have an error: TS2461: Type 'T' is not an array type.

So, I tried :

export const sort= <T>(array?: ArrayLike<T> | null) => {
  if (isNil(array)) return;
  return [...array].sort((a, b) => {
    return Date.parse(b.creation_date) - Date.parse(a.creation_date);
  });
};

and here is another error: TS2461: Type 'ArrayLike' is not an array type.

So, how do I write a generic function?

CodePudding user response：

Your type hint does not guarantee that the "array" parameter is actually an array. Since you use a generic, I can pass any value in there, like a number, and it will pass the null check and try to spread that number, resulting in an error.

The way I would do it is to check if the parameter is an array instead of checking if it's not null, like this:

const sort = <T>(array?: T | null) => {
    if (Array.isArray(array)) {
        return [...array].sort((a, b) => Date.parse(b.creation_date) - Date.parse(a.creation_date));
    };

    return;
};

CodePudding user response：

Please try to use as follows:

export const sort= <Type>(array?: Type[] | null) => {
  if (isNil(array)) return;
  return [...array].sort((a, b) => {
    return Date.parse(b.creation_date) - Date.parse(a.creation_date);
  });
};

CodePudding user response：

Use T as the element type and write

export const sort= <T>(array?: T[] | null) => {
  if (isNil(array)) return;
  return [...array].sort((a, b) => {
    return Date.parse(b.creation_date) - Date.parse(a.creation_date);
  });
};