Better typings for Array.map()

Author: jablko

src/lib/es5.d.ts

@@ -1138,7 +1138,7 @@ interface ReadonlyArray<T> {
      * @param callbackfn A function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.
      * @param thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
      */
-    map<U>(callbackfn: (value: T, index: number, array: readonly T[]) => U, thisArg?: any): U[];
+    map<U>(callbackfn: (value: T, index: number, array: readonly T[]) => U, thisArg?: any): { -readonly [P in keyof this]: U };
     /**
      * Returns the elements of an array that meet the condition specified in a callback function.
      * @param callbackfn A function that accepts up to three arguments. The filter method calls the callbackfn function one time for each element in the array.
@@ -1308,7 +1308,7 @@ interface Array<T> {
      * @param callbackfn A function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.
      * @param thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
      */
-    map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): U[];
+    map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): { -readonly [P in keyof this]: U };
     /**
      * Returns the elements of an array that meet the condition specified in a callback function.
      * @param callbackfn A function that accepts up to three arguments. The filter method calls the callbackfn function one time for each element in the array.