Why can't I set the 'prototype' of a function created using 'bind'?

Question

Consider this code:

function foo(something) {
  this.a = something;
}

var obj1 = {};

var bar = foo.bind(obj1);

Now the following statement doesn't execute:

bar.prototype.newprop = "new"; // Cannot execute this

As I understood, every function has a prototype object. Then why can't we execute the above statement?

And bar is indeed a function as we can call it:

bar(2);
console.log(obj1.a); // 2

Answer 1

As I understood, every function has a prototype object.

Well, there are exceptions to every rule :-) You found one: bound functions don't have a .prototype property because they don't need it. When you call a bound function with new, it calls the original function as a constructor, using the original's .prototype object as the prototype of the new instance.

In fact, since ECMAScript 6 many functions don't have a .prototype property with an object, because they are not constructors - they cannot be called with new so they don't need it. Among those are

• arrow functions (() => {…})
• methods (method() { … } in object literals and classes)
• builtin non-constructor functions (like Math.sin)