javascript - Null prototype, Object.prototype and Object.create -

why setting prototype property of constructor function null not prevent objects created function calling through methods on object.prototype, in same way setting prototype object.create(null) does?

that is, why case:

function foo(){} foo.prototype = null; console.log(new foo().tostring); //outputs function tostring() { [native code] } (or whatever)  function foo(){} foo.prototype = object.create(null); console.log(new foo().tostring); //output undefined 

in short

yes, observation correct - function constructed new operator always have object prototype in case object.prototype , indeed unlike function created object.create.

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on why

one can see behavior specified in es5 language specification on javascript based on. let's see this.

in new:

quoting specification of [[construct]] method of functions indicates how object creation using new operator performed can see following specified:

if type(proto) not object, set [[prototype]] internal property of obj standard built-in object prototype object described in 15.2.4.

in object.create:

on other hand, if check out the spec object.create can see object.create(o) specifies:

set [[prototype]] internal property of obj o.

which means can set it, explicitly checks null or object in algorithm (please do follow link spec , read :))

so prototype of objects called new foo object.prototype , not null. impossible create objects no prototype without object.create using standard methods only.