Typescript destructuring with required parameter

You use a default value {} for the PageConfig constructor argument, but you marked getList as required in the type. If I understand you correctly, you want to have the constructor argument and getList always set, so change your code to:

export class PageConfig {
  constructor({
    getList,
    isSliding = false
  }: {
    getList: (pagingInfo: PagingInfo) => Observable<any>;
    isSliding?: boolean;
  }) {
    … // use getList and isSliding
  }
}

This syntax (destructuring with default values) can be a bit cumbersome sometimes. It gets clearer, when you extract the constructor argument type.

TypeScript docs example

You want to remove the default, and also change the parameter order - required parameters always come before optional parameters:

constructor(getList: (pagingInfo: PagingInfo) => Observable<any>, isSliding?: boolean = false) {...}

One option if it is the case that all constructor parameters are optional/have a default value would be simply to use a Partial config in the constructor and merge with defaults, e.g.

interface IPageConfigConstructor {
  isSliding: boolean;
  getList: (pagingInfo) => Observable<any>;
}
const DEFAULT_CONFIG:IPageConfigConstructor = {
  isSliding: true,
  getList: (pagingInfo) => null
}

class PageConfig {
  constructor(config: Partial<IPageConfigConstructor>) {
    const mergedConfig:IPageConfigConstructor = {...DEFAULT_CONFIG,...config}
  }
}

class UsersPage {
  config = new PageConfig({getList:(pagingInfo)=>this.getList(pagingInfo)});

  getList(pagingInfo) {
    // do work...
    return new Observable
  }
}