Define function inside prototype(like toString function)

Question

When I managed to define a function inside prototype object, but when I use foreach loop on the props I found this method as one of my props either.

I wanted to know if I can define methods like the toString() mehtod?

the hasOwnProperty() if inside the loop is not an option for me because the loop is inside a package.

Here is my code.

function Person (personProps) {

    Object.assign(this, {...personProps});
    console.log(this);
}

Person.prototype.sayHay = () => {
    console.log("hay");

}


const createPerson = (personProps) => {
    let x = new Person(personProps);
    x.sayHay();
    return x;
};

export default createPerson;

Thanks for helping.

Look into `Object.defineProperty` https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty — evolutionxbox, Aug 16 '17 at 13:36
"*when i do foreach on the props*" - please show us where you're doing that and why. Btw, there's no `forEach` that loops over properties? — Bergi, Aug 16 '17 at 17:31

Yasser Hussain · Answer 1 · 2017-08-16T17:20:34.163

You can define property on the Person prototype like so -

function Person(personProps) {
  Object.assign(this, { ...personProps});
}

Object.defineProperty(Person.prototype, "sayHay", {
  value: function() {
    console.log("hay");
  },
  /* 
     You can make `enumerable` property below false, 
     if you don't want it to be shown while 
     looping over properties
  */
  enumerable: true 
});

const createPerson = (personProps) => {
  let x = new Person(personProps);
  return x;
};

let person = createPerson({
  a: 1
})

person.sayHay();

for (p in person) {
  console.log(p);
}

This way you don't have to define sayHay property each time you create the object.

score 0 · Answer 2 · answered Aug 16 '17 at 13:37

0

You can use a class

class Person {
  constructor(personProps) {
    Object.assign(this, { ...personProps});
  }

  sayHay() {
    console.log("hay");
  }
}

const createPerson = (personProps) => {
  let x = new Person(personProps);
  x.sayHay();
  return x;
};

let person = createPerson({
  name: 'John'
});

for (prop in person) {
  console.log(prop);
}

answered Aug 16 '17 at 13:37

Serge K.

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my problem in this solution is that i dont want the Person to have functions refs. and also i need to send does Persons to the server side without the functions – Goor Lavi Aug 16 '17 at 13:41
1

_"i dont want the Person to have functions refs."_ What do you mean ? – Serge K. Aug 16 '17 at 13:51
oh im sorry. i ment i want the Person to have functions references*. i dont want a function per instance – Goor Lavi Aug 16 '17 at 13:55
Not sure what you mean, but look at @evolutionxbox comment, it should guide you to another solution – Serge K. Aug 16 '17 at 13:57
2

@GoorLavi Using a `class` doesn't create a function per instance. It's still on the prototype, just not enumerable by default. – Bergi Aug 16 '17 at 17:32

Define function inside prototype(like toString function)

2 Answers2