Improve typing of 'bind' method on function types

Author: ahejlsberg

src/lib/es5.d.ts

@@ -295,6 +295,16 @@ interface FunctionConstructor {
 
 declare const Function: FunctionConstructor;
 
+/**
+ * Extracts the type of the 'this' parameter of a function type, or 'unknown' if the function type has no 'this' parameter.
+ */
+type ThisParameterType<T> = T extends (this: unknown, ...args: any[]) => any ? unknown : T extends (this: infer U, ...args: any[]) => any ? U : unknown;
+
+/**
+ * Removes the 'this' parameter from a function type.
+ */
+type OmitThisParameter<T> = unknown extends ThisParameterType<T> ? T : T extends (...args: infer A) => infer R ? (...args: A) => R : T;
+
 interface CallableFunction extends Function {
     /**
       * Calls the function with the specified object as the this value and the elements of specified array as the arguments.
@@ -317,7 +327,7 @@ interface CallableFunction extends Function {
       * @param thisArg The object to be used as the this object.
       * @param args Arguments to bind to the parameters of the function.
       */
-    bind<T, A extends any[], R>(this: (this: T, ...args: A) => R, thisArg: T): (...args: A) => R;
+    bind<T>(this: T, thisArg: ThisParameterType<T>): OmitThisParameter<T>;
     bind<T, A0, A extends any[], R>(this: (this: T, arg0: A0, ...args: A) => R, thisArg: T, arg0: A0): (...args: A) => R;
     bind<T, A0, A1, A extends any[], R>(this: (this: T, arg0: A0, arg1: A1, ...args: A) => R, thisArg: T, arg0: A0, arg1: A1): (...args: A) => R;
     bind<T, A0, A1, A2, A extends any[], R>(this: (this: T, arg0: A0, arg1: A1, arg2: A2, ...args: A) => R, thisArg: T, arg0: A0, arg1: A1, arg2: A2): (...args: A) => R;
@@ -347,7 +357,7 @@ interface NewableFunction extends Function {
       * @param thisArg The object to be used as the this object.
       * @param args Arguments to bind to the parameters of the function.
       */
-    bind<A extends any[], R>(this: new (...args: A) => R, thisArg: any): new (...args: A) => R;
+    bind<T>(this: T, thisArg: any): T;
     bind<A0, A extends any[], R>(this: new (arg0: A0, ...args: A) => R, thisArg: any, arg0: A0): new (...args: A) => R;
     bind<A0, A1, A extends any[], R>(this: new (arg0: A0, arg1: A1, ...args: A) => R, thisArg: any, arg0: A0, arg1: A1): new (...args: A) => R;
     bind<A0, A1, A2, A extends any[], R>(this: new (arg0: A0, arg1: A1, arg2: A2, ...args: A) => R, thisArg: any, arg0: A0, arg1: A1, arg2: A2): new (...args: A) => R;