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ae-missing-getter

"The property ___ has a setter but no getter."

Remarks​

TypeScript properties are conventionally used to indicate an API that behaves similar to reading or writing a variable. For example, style guides often recommend:

  • property getters shouldn't perform expensive/complex operations
  • property getters shouldn't cause observable side-effects (e.g. reading the property moves a stream pointer forwards)
  • property getters should avoid throwing exceptions

In the same way, it would be strange to declare a property getter without a setter. After assigning a value to a variable, intuitively a developer would expect to be able to read the assigned value.

Consider this example:

/**
 * Represents a book from the catalog.
 * @public
 */
export class Book {
  private _title: string = 'untitled';

  /**
   * Sets the title of the book.
   */
  // Error: (ae-missing-getter) The property "title" has a setter but no getter.
  public set title(value: string) {
    this._title = value;
  }
}

const book: Book = new Book();
book.title = 'The Hobbit';
console.log('The title: ' + book.title); // prints "The title: undefined"

The above behavior is counterintuitive. The missing setter is likely a mistake in the API design. API Extractor reports the ae-missing-getter error.

How to fix​

The simplest solution is to implement the missing property getter. Note that the getter's documentation describes both operations; a property setter cannot have a doc comment:

/**
 * Represents a book from the catalog.
 * @public
 */
export class Book {
  private _title: string = 'untitled';

  /**
   * Gets or sets the title of the book.
   */
  public get title(): string {
    return this._title;
  }

  public set title(value: string) {
    this._title = value;
  }
}

const book: Book = new Book();
book.title = 'The Hobbit';
console.log('Title: ' + book.title); // prints "Title: The Hobbit"

Alternatively, if your API really needs to be a unidirectional operation, you should design it as a method instead of a property:

/**
 * Represents a book from the catalog.
 * @public
 */
export class Book {
  private _title: string = 'untitled';

  /**
   * Sets the title of the book.
   */
  public setTitle(title: string): void {
    this._title = title;
  }
}

A pitfall involving "inherited" getters

If you choose to disable the ae-missing-getter validation, be careful with inherited properties: If a child class overrides a property by specifying the setter only, the getter will become undefined. Unlike some other languages, ECMAScript get and set attributes comprise a single accessor property that is being overridden. See this playground link for an example.

See also​