Re: Class prototype readonly

[Nicholas Zakas]

Nicholas, not Nic. :)

The prototype property cannot be overwritten, so PersonClass.prototype cannot be set to a different object. The prototype can still be modified.

for-in iterates over both own and prototype properties that are enumerable. getOwnPropertyNames returns only own properties but returns both enumerable and non enumerable properties. 

On Wed, Apr 29, 2020 at 8:20 PM Jeff <zhenzh...@gmail.com> wrote:

Hi Nic,

1st question, On page 167, the only note says the prototype of a class is readonly, but I tried with following code, it works well,

class PersonClass {

constructor(name) {

this.name = name;

}

sayName() {

console.log(this.name);

}

}

/* method or property could be assigned on the prototype

same as declaring class with function */

PersonClass.prototype.anotherFunc = function () {

console.log(this, 'another func');

};

PersonClass.prototype.age = 9;

let person = new PersonClass('jeff');

/* special note: for-in and getOwnPropertyNames are diff

for-in only gets props on prototype, getOwnPropertyNames

only gets instance attr */

for (const key in person) {

console.log(key);

}

console.log(Object.getOwnPropertyNames(person));

2nd question, as my comments show, for-in only gets all the props on prototype of a class, and Object.getOwnPropertyNames only gets attrs on the instance. I am asking that cuz you probably know it and I couldn't find a good answer for that online. 

thx & brs,

Jeff

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[Jeff]

Thanks Nicolas :-)

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