Strengthen type of methods accepting thisArg.

Strengthen forEach, filter, map, from, find, findIndex to be more
stricter, so that the TypeScript compiler can understand the type of
this when thisArg is used but the predicate does not explicitly mention
the type of this and only be implicit.

Although methods like some, every also have the thisArg as its parameter
but is not included in this change, because in some places those are
called like e.g. array.some(isNaN) and in these cases, the TSC does not
understand the type of the isNaN is actually a subtype.

Also, this excludes to improve the methods cases where the interface has
overloads of the same method, due to the bug
microsoft#44373, as the current TSC
cannot resolve multiple declarations properly for cases which these
functions are called on a union of types which all are arrays. e.g.
(string[]|number[]).forEach(predicate, ...);

Author: h-joo

lib/lib.es2015.collection.d.ts

@@ -28,7 +28,7 @@ interface Map<K, V> {
     /**
      * Executes a provided function once per each key/value pair in the Map, in insertion order.
      */
-    forEach(callbackfn: (value: V, key: K, map: Map<K, V>) => void, thisArg?: any): void;
+    forEach<T>(callbackfn: (this: T, value: V, key: K, map: Map<K, V>) => void, thisArg?: T): void;
     /**
      * Returns a specified element from the Map object. If the value that is associated to the provided key is an object, then you will get a reference to that object and any change made to that object will effectively modify it inside the Map.
      * @returns Returns the element associated with the specified key. If no element is associated with the specified key, undefined is returned.
@@ -56,7 +56,7 @@ interface MapConstructor {
 declare var Map: MapConstructor;
 
 interface ReadonlyMap<K, V> {
-    forEach(callbackfn: (value: V, key: K, map: ReadonlyMap<K, V>) => void, thisArg?: any): void;
+    forEach<T>(callbackfn: (this: T, value: V, key: K, map: ReadonlyMap<K, V>) => void, thisArg?: T): void;
     get(key: K): V | undefined;
     has(key: K): boolean;
     readonly size: number;
@@ -104,7 +104,7 @@ interface Set<T> {
     /**
      * Executes a provided function once per each value in the Set object, in insertion order.
      */
-    forEach(callbackfn: (value: T, value2: T, set: Set<T>) => void, thisArg?: any): void;
+    forEach<K>(callbackfn: (this: K, value: T, value2: T, set: Set<T>) => void, thisArg?: K): void;
     /**
      * @returns a boolean indicating whether an element with the specified value exists in the Set or not.
      */
@@ -122,7 +122,7 @@ interface SetConstructor {
 declare var Set: SetConstructor;
 
 interface ReadonlySet<T> {
-    forEach(callbackfn: (value: T, value2: T, set: ReadonlySet<T>) => void, thisArg?: any): void;
+    forEach<K>(callbackfn: (this: K, value: T, value2: T, set: ReadonlySet<T>) => void, thisArg?: K): void;
     has(value: T): boolean;
     readonly size: number;
 }

lib/lib.es2015.iterable.d.ts

@@ -88,7 +88,7 @@ interface ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from<T, U>(iterable: Iterable<T> | ArrayLike<T>, mapfn: (v: T, k: number) => U, thisArg?: any): U[];
+    from<T, U, K = undefined>(iterable: Iterable<T> | ArrayLike<T>, mapfn: (this: K, v: T, k: number) => U, thisArg?: K): U[];
 }
 
 interface ReadonlyArray<T> {
@@ -265,7 +265,7 @@ interface Int8ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Int8Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Int8Array;
 }
 
 interface Uint8Array {
@@ -293,7 +293,7 @@ interface Uint8ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Uint8Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: T): Uint8Array;
 }
 
 interface Uint8ClampedArray {
@@ -324,7 +324,7 @@ interface Uint8ClampedArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Uint8ClampedArray;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Uint8ClampedArray;
 }
 
 interface Int16Array {
@@ -354,7 +354,7 @@ interface Int16ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Int16Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Int16Array;
 }
 
 interface Uint16Array {
@@ -382,7 +382,7 @@ interface Uint16ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Uint16Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Uint16Array;
 }
 
 interface Int32Array {
@@ -410,7 +410,7 @@ interface Int32ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Int32Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Int32Array;
 }
 
 interface Uint32Array {
@@ -438,7 +438,7 @@ interface Uint32ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Uint32Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Uint32Array;
 }
 
 interface Float32Array {
@@ -466,7 +466,7 @@ interface Float32ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Float32Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Float32Array;
 }
 
 interface Float64Array {
@@ -494,5 +494,5 @@ interface Float64ArrayConstructor {
      * @param mapfn A mapping function to call on every element of the array.
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
-    from(arrayLike: Iterable<number>, mapfn?: (v: number, k: number) => number, thisArg?: any): Float64Array;
+    from<T>(arrayLike: Iterable<number>, mapfn?: (this: T, v: number, k: number) => number, thisArg?: T): Float64Array;
 }

lib/lib.es2020.bigint.d.ts

@@ -202,7 +202,7 @@ interface BigInt64Array {
      * @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(predicate: (value: bigint, index: number, array: BigInt64Array) => any, thisArg?: any): BigInt64Array;
+    filter<T>(predicate: (this: T, value: bigint, index: number, array: BigInt64Array) => any, thisArg?: T): BigInt64Array;
 
     /**
      * Returns the value of the first element in the array where predicate is true, and undefined
@@ -213,7 +213,7 @@ interface BigInt64Array {
      * @param thisArg If provided, it will be used as the this value for each invocation of
      * predicate. If it is not provided, undefined is used instead.
      */
-    find(predicate: (value: bigint, index: number, array: BigInt64Array) => boolean, thisArg?: any): bigint | undefined;
+    find<T>(predicate: (this: T, value: bigint, index: number, array: BigInt64Array) => boolean, thisArg?: T): bigint | undefined;
 
     /**
      * Returns the index of the first element in the array where predicate is true, and -1
@@ -224,7 +224,7 @@ interface BigInt64Array {
      * @param thisArg If provided, it will be used as the this value for each invocation of
      * predicate. If it is not provided, undefined is used instead.
      */
-    findIndex(predicate: (value: bigint, index: number, array: BigInt64Array) => boolean, thisArg?: any): number;
+    findIndex<T>(predicate: (this: T, value: bigint, index: number, array: BigInt64Array) => boolean, thisArg?: T): number;
 
     /**
      * Performs the specified action for each element in an array.
@@ -233,7 +233,7 @@ interface BigInt64Array {
      * @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.
      */
-    forEach(callbackfn: (value: bigint, index: number, array: BigInt64Array) => void, thisArg?: any): void;
+    forEach<T>(callbackfn: (this: T, value: bigint, index: number, array: BigInt64Array) => void, thisArg?: T): void;
 
     /**
      * Determines whether an array includes a certain element, returning true or false as appropriate.
@@ -279,7 +279,7 @@ interface BigInt64Array {
      * @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(callbackfn: (value: bigint, index: number, array: BigInt64Array) => bigint, thisArg?: any): BigInt64Array;
+    map<T>(callbackfn: (this: T, value: bigint, index: number, array: BigInt64Array) => bigint, thisArg?: T): BigInt64Array;
 
     /**
      * Calls the specified callback function for all the elements in an array. The return value of
@@ -411,7 +411,7 @@ interface BigInt64ArrayConstructor {
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
     from(arrayLike: ArrayLike<bigint>): BigInt64Array;
-    from<U>(arrayLike: ArrayLike<U>, mapfn: (v: U, k: number) => bigint, thisArg?: any): BigInt64Array;
+    from<U, T = undefined>(arrayLike: ArrayLike<U>, mapfn: (this: T, v: U, k: number) => bigint, thisArg?: T): BigInt64Array;
 }
 
 declare var BigInt64Array: BigInt64ArrayConstructor;
@@ -474,7 +474,7 @@ interface BigUint64Array {
      * @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(predicate: (value: bigint, index: number, array: BigUint64Array) => any, thisArg?: any): BigUint64Array;
+    filter<T>(predicate: (this: T, value: bigint, index: number, array: BigUint64Array) => any, thisArg?: T): BigUint64Array;
 
     /**
      * Returns the value of the first element in the array where predicate is true, and undefined
@@ -485,7 +485,7 @@ interface BigUint64Array {
      * @param thisArg If provided, it will be used as the this value for each invocation of
      * predicate. If it is not provided, undefined is used instead.
      */
-    find(predicate: (value: bigint, index: number, array: BigUint64Array) => boolean, thisArg?: any): bigint | undefined;
+    find<T>(predicate: (this: T, value: bigint, index: number, array: BigUint64Array) => boolean, thisArg?: T): bigint | undefined;
 
     /**
      * Returns the index of the first element in the array where predicate is true, and -1
@@ -496,7 +496,7 @@ interface BigUint64Array {
      * @param thisArg If provided, it will be used as the this value for each invocation of
      * predicate. If it is not provided, undefined is used instead.
      */
-    findIndex(predicate: (value: bigint, index: number, array: BigUint64Array) => boolean, thisArg?: any): number;
+    findIndex<T>(predicate: (this: T, value: bigint, index: number, array: BigUint64Array) => boolean, thisArg?: T): number;
 
     /**
      * Performs the specified action for each element in an array.
@@ -505,7 +505,7 @@ interface BigUint64Array {
      * @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.
      */
-    forEach(callbackfn: (value: bigint, index: number, array: BigUint64Array) => void, thisArg?: any): void;
+    forEach<T>(callbackfn: (this: T, value: bigint, index: number, array: BigUint64Array) => void, thisArg?: T): void;
 
     /**
      * Determines whether an array includes a certain element, returning true or false as appropriate.
@@ -551,7 +551,7 @@ interface BigUint64Array {
      * @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(callbackfn: (value: bigint, index: number, array: BigUint64Array) => bigint, thisArg?: any): BigUint64Array;
+    map<T>(callbackfn: (this: T, value: bigint, index: number, array: BigUint64Array) => bigint, thisArg?: T): BigUint64Array;
 
     /**
      * Calls the specified callback function for all the elements in an array. The return value of
@@ -683,7 +683,7 @@ interface BigUint64ArrayConstructor {
      * @param thisArg Value of 'this' used to invoke the mapfn.
      */
     from(arrayLike: ArrayLike<bigint>): BigUint64Array;
-    from<U>(arrayLike: ArrayLike<U>, mapfn: (v: U, k: number) => bigint, thisArg?: any): BigUint64Array;
+    from<U, T = undefined>(arrayLike: ArrayLike<U>, mapfn: (this: T, v: U, k: number) => bigint, thisArg?: T): BigUint64Array;
 }
 
 declare var BigUint64Array: BigUint64ArrayConstructor;