How are static methods defined on constructor functions in javascript?

Question

Refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object

So Object is a constructor function and here I see 2 types of methods defined -

Static methods - Object.create(), Object.assign() ...
Instance methods - Object.prototype.hasOwnProperty() ...

I understand how Instance methods are defined and used but no idea about static methods -

function Person() { }

Person.prototype.greetInstance = function () { return 'Hello!' };

let p1 = new Person();
console.log(p1.greetInstance()) // Hello!
console.log(Person.greetStatic()) // where should I define so this works ?? 🤷‍♂️

Can someone please explain how to define greetStatic() ?

Person.greetStatic = function() { };?

StriplingWarrior
– StriplingWarrior

2021-07-16 21:07:53 +00:00
Commented Jul 16, 2021 at 21:07 — StriplingWarrior
– StriplingWarrior, Commented Jul 16, 2021 at 21:07
Perhaps you should refer to these docs instead.

Tyler2P
– Tyler2P

2021-07-16 21:11:12 +00:00
Commented Jul 16, 2021 at 21:11 — Tyler2P
– Tyler2P, Commented Jul 16, 2021 at 21:11
ok thank you. That was something silly I missed.

mustafa1993
– mustafa1993

2021-07-16 21:28:05 +00:00
Commented Jul 16, 2021 at 21:28 — mustafa1993
– mustafa1993, Commented Jul 16, 2021 at 21:28

Emiel Zuurbier · Accepted Answer · 2021-07-16 21:09:17Z

2

Static properties or methods are just properties and methods that are defined on the object itself and not the prototype.

function Person() { }

Person.greetStatic = function() { return 'Static hello!' }
Person.prototype.greetInstance = function () { return 'Hello!' };

let p1 = new Person();
console.log(p1.greetInstance()) 
console.log(Person.greetStatic())

Using the class syntax might help make this more clear, as you can use the static keyword in it. It's just syntactic sugar and he result will be exactly the same.

class Person {
  static greetStatic() {
    return 'Static hello!';
  }
  
  greetInstance() {
    return 'Hello!';
  }
}

let p1 = new Person();
console.log(p1.greetInstance()) 
console.log(Person.greetStatic())

answered Jul 16, 2021 at 21:09

Emiel Zuurbier

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2 Comments

mustafa1993 Over a year ago

yes but class being syntactic sugar is what makes it harder to understand. How do I define method on "Person" (without using class). Using dot notation? is it same as static in class?

Emiel Zuurbier Over a year ago

@mustafa1993 A function is little more than an object. So setting a static function is the same as assigning a function to a property. Using the dot notation is one way to do it and a very valid one. The bracket notation Person['greetStatic'] = function () {} does exactly the same. Object.defineProperty() allows for more options to be set, but in the end has the same goal.

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