TS2683 (TS) 'this' implicitly has type 'any' because it does not have a type annotation

Question

I'm facing this problem with TypeScript file and would like to know how to fix this.

For now I have suppressed this typescript exception but would like to learn how to address this. The following is my code:

export class BaseResult {     isSuccessful: boolean;     totalRecords: number;     successMessage: string;     reasonForFailure: string;     lastExecutedDateTime: Date; }  export class Result<T> extends BaseResult {     data: T; }  export class CollectionResult<T> extends BaseResult {     data: T[]; }  export class PagedCollectionResult<T> extends CollectionResult<T> {     pageNumber: number;     pageSize: number;     filter: string;      pages = function () {         return (this.totalRecords <= 0 || this.pageSize <= 0) ? 0 : Math.ceil(this.totalRecords / this.pageSize);//<--All the **this** keyword shows the error     } } 

Answer 1

As some of the comments indicated, your this reference is not typed because you are using the function () {} syntax to define your function. The this object inside such a function will inherently be of type any , because this will be the caller of the function (unknowable at design-time).

If you change your syntax to an arrow function, like

pages = () => { 

or simply omit the function keyword and arrow altogether, like

pages() { 

then the this object inside the function will reference the class instance this instead of type any.

See the TypeScript handbook for more explanation.

Answer 2

Use explicit this annotation:

pages = function(this: BaseResult) { 

In this context, this is not an argument to the function but the actual place to declare the type of this, see the handbook:

The JavaScript specification states that you cannot have a parameter called this, and so TypeScript uses that syntax space to let you declare the type for this in the function body.

https://www.typescriptlang.org/docs/handbook/2/functions.html#declaring-this-in-a-function