I have a simple example like

    interface employer {
      name: string;
      age: number;
    }

    const arr: employer[] = [{name:'Amy',age:18},{name:'Bob',age:20}];

    let data = arr.reduce((c, b) =>  b.age > 18 ? [...c, b] : c,[])

    console.log(data)

I just want to filer arr array and return the age of the person is higher than 18 for example But I get errors

No overload matches this call.
  Overload 1 of 3, '(callbackfn: (previousValue: employer, currentValue: employer, currentIndex: number, array: employer[]) => employer, initialValue: employer): employer', gave the following error.
    Type 'employer[]' is missing the following properties from type 'employer': name, age
  Overload 2 of 3, '(callbackfn: (previousValue: never[], currentValue: employer, currentIndex: number, array: employer[]) => never[], initialValue: never[]): never[]', gave the following error.
    Type 'employer[]' is not assignable to type 'never[]'.
      Type 'employer' is not assignable to type 'never'.

For this b.age > 18 ? [...c, b] : c I think it worked for javascript How can we fix it? Thanks

CodePudding user response：

In order to fix this error, you need to add type on the reduce function. You can do this by calling

let data = arr.reduce<employer[]>((c, b) =>  b.age > 18 ? [...c, b] : c,[])

also, this is valid

let data = arr.reduce((c, b) =>  b.age > 18 ? [...c, b] : c,[] as employer[])

but I think the first one looks better.

You can find a working example in this playground

CodePudding user response：

I try another way

interface employer { 
      name: string; 
      age: number; 
    } 
 
    const arr: employer[] = [{name:'Amy',age:18},{name:'Bob',age:20}]; 
 
    let data = arr.reduce((c:any, b:any) =>  b.age > 18 ? [...c, b] : c,[]) 
 
    console.log(arr)