lib.es5.d.ts

/** See https://stackoverflow.com/a/51390763/1470607  */
type Falsy = false | 0 | '' | null | undefined;

/**
 * see https://www.karltarvas.com/typescript-array-filter-boolean.html
 */
interface Array<T> {
  /**
   * Returns the elements of an array that meet the condition specified in a
   * callback function.
   * @param predicate A function that accepts up to three arguments. The filter
   * method calls the predicate function one time for each element in the array.
   * @param thisArg An object to which the this keyword can refer in the
   * predicate function. If thisArg is omitted, undefined is used as the
   * this value.
   */
  filter<S extends T>(predicate: BooleanConstructor, thisArg?: any)
    : Exclude<S, Falsy>[];
}