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Private properties in JavaScript ES6 classes
(41 answers)
Closed 6 years ago.
In ES5, you could emulate a class with private and public variables like this:
car.js
function Car() {
// using var causes speed to be only available inside Car (private)
var speed = 10;
// public variable - still accessible outside Car
this.model = "Batmobile";
// public method
this.init = function(){
}
}
But in ES6, you can no longer declare vars outside the constructor, making it actually HARDER to work with classes in a OOP way!?
You can declare variables in the constructor using this, but that makes them public by default. This is very weird since ES6 DOES have a get / set keyword!
class Vehicle {
constructor(make, year) {
// the underscore is nice, but these are still public!
this._make = make;
this._year = year;
}
// get and set can be handy, but would make more sense
// if _make and _year were not accessible any other way!
get make() {
return this._make;
}
get year() {
return this._year;
}
}
ES6 standard does not offer a new way for defining private variables.
It's a fact, that new ES6 class is simply syntactic sugar around regular prototype-based constructors.
get and set keywords are offering a way for simplified definition of ES5 custom getters and setters that were previously defined with a descriptor of Object.defineProperty()
The best you could do is to use those techniques with Symbols or WeakMaps
The example below features the use of a WeakMap for storing private properties.
// myModule.js
const first_name = new WeakMap();
class myClass {
constructor (firstName) {
first_name.set(this, firstName);
}
get name() {
return first_name.get(this);
}
}
export default myClass;
I'm referring to article, written by David Vujic What? Wait. Really? Oh no! (a post about ES6 classes and privacy) with the idea of using WeakMaps.
The same way than in ES5: define the methods that must access the private variables in the constructor instead of the prototype, thus making them privileged methods.
Otherwise there in no good way to allow prototypical methods to access private data, but still hide it from the outside. You can try symbols, weakmaps or handshakes, but IMO none is perfect. See accessing private member variables from prototype-defined functions for some ideas.
But in ES6, you can no longer declare vars outside the constructor
And you don't need to. You didn't do it in your ES5 constructor either. You can translate your code literally to
class Car {
constructor() {
// local variable
var speed = 10;
// public property
this.model = "Batmobile";
// public method
this.init = () => {
…
}; // using an arrow function here simplifies things
}
}
Update January 2016 - whilst I found the approach given in the accepted answer correct, I would like to state that using modules and symbols is an effective information hiding technique in ES2015+ (but Class attributes using Symbols will be hidden, not strictly private).
An effective, lightweight information hiding can be achieved through a combination of ES2015 modules (which would only export what you declare as exported) and ES2015 symbols. Symbol is a new built-in type. Every new Symbol value is unique. Hence can be used as a key on an object.
If the client calling code doesn't know the symbol used to access that key, they can't get hold of it since the symbol is not exported.
Quick example using your code:
vehicle.js
const s_make = Symbol();
const s_year = Symbol();
export class Vehicle {
constructor(make, year) {
this[s_make] = make;
this[s_year] = year;
}
get make() {
return this[s_make];
}
get year() {
return this[s_year];
}
}
and to use the module vehicle.js
client.js
import {Vehicle} from './vehicle';
const vehicle1 = new Vehicle('Ford', 2015);
console.log(vehicle1.make); //Ford
console.log(vehicle1.year); // 2015
However, symbols although unique, are not actually private since they are exposed via reflection features like Object.getOwnPropertySymbols...
const vals = Object.getOwnPropertySymbols(vehicle1);
vehicle1[vals[0]] = 'Volkswagon';
vehicle1[vals[1]] = 2013;
console.log(vehicle1.make); // Volkswagon
console.log(vehicle1.year); // 2013
Takeaway message - Modules in general are a great way to hide something because if not exported then not available for use outside the module, and used with privately stored Symbols to act as the keys, then class attributes too can become hidden (but not necessarily private). Class declarations are particularly well suited when considered as part of well constructed modules (amd, commonjs, or es6/2015).
Related
I'm looking at implementation of private members in TypeScript, and I find it a little confusing. Intellisense doesn't allow to access private member, but in pure JavaScript, it's all there. This makes me think that TS doesn't implement private members correctly.
Any thoughts?
class Test{
private member: any = "private member";
}
alert(new Test().member);
Just as with the type checking, the privacy of members are only enforced within the compiler.
A private property is implemented as a regular property, and code outside the class is not allowed to access it.
To make something truly private inside the class, it can't be a member of the class, it would be a local variable created inside a function scope inside the code that creates the object. That would mean that you can't access it like a member of the class, i.e. using the this keyword.
JavaScript does support private variables.
function MyClass() {
var myPrivateVar = 3;
this.doSomething = function() {
return myPrivateVar++;
}
}
In TypeScript this would be expressed like so:
class MyClass {
doSomething: () => number;
constructor() {
var myPrivateVar = 3;
this.doSomething = function () {
return myPrivateVar++;
}
}
}
EDIT
This approach should only be used SPARINGLY where it is absolutely needed. For example if you need to cache a password temporarily.
There are performance costs to using this pattern (irrelevant of Javascript or Typescript) and should only be used where absolutely necessary.
Since TypeScript 3.8 will be released you will be able to declare private field which can’t be accessed or even detected outside of the containing class.
class Person {
#name: string
constructor(name: string) {
this.#name = name;
}
greet() {
console.log(`Hello, my name is ${this.#name}!`);
}
}
let jeremy = new Person("Jeremy Bearimy");
jeremy.#name
// ~~~~~
// Property '#name' is not accessible outside class 'Person'
// because it has a private identifier.
Private fields starts with # character
Please note that these private fields will be something different than fields marked with private keyword
Ref. https://devblogs.microsoft.com/typescript/announcing-typescript-3-8-beta/
Once support for WeakMap is more widely available there is an interesting technique detailed in example #3 here.
It allows for private data AND avoids the performance costs of Jason Evans example by allowing the data to be accessible from prototype methods instead of only instance methods.
The linked MDN WeakMap page lists browser support at Chrome 36, Firefox 6.0, IE 11, Opera 23, and Safari 7.1.
let _counter = new WeakMap();
let _action = new WeakMap();
class Countdown {
constructor(counter, action) {
_counter.set(this, counter);
_action.set(this, action);
}
decrement() {
let counter = _counter.get(this);
if (counter < 1) return;
counter--;
_counter.set(this, counter);
if (counter === 0) {
_action.get(this)();
}
}
}
Thanks to Sean Feldman for the link to the official discussion on this issue - see his answer for the link.
I read the discussion he linked to, and here's a summary of the key points:
Suggestion: private properties in constructor
problems: can't access from prototype functions
Suggestion: private methods in constructor
problems: same as with properties, plus you lose the performance benefit of creating a function once per class in the prototype; instead you create a copy of the function for each instance
Suggestion: add boilerplate to abstract property access and enforce visibility
problems: major performance overhead; TypeScript is designed for large applications
Suggestion: TypeScript already wraps the constructor and prototype method definitions in a closure; put private methods and properties there
problems with putting private properties in that closure: they become static variables; there is not one per instance
problems with putting private methods in that closure: they do not have access to this without some sort of workaround
Suggestion: automatically mangle the private variable names
counter arguments: that's a naming convention, not a language construct. Mangle it yourself
Suggestion: Annotate private methods with #private so minifiers that recognize that annotation can effectively minify the method names
No significant counter arguments to this one
Overall counter-arguments to adding visibility support in emitted code:
the problem is that JavaScript itself doesn't have visibility modifiers - this isn't TypeScript's problem
there is already an established pattern in the JavaScript community: prefix private properties and methods with an underscore, which says "proceed at your own risk"
when TypeScript designers said that truly private properties and methods aren't "possible", they meant "not possible under our design constraints", specifically:
The emitted JS is idiomatic
Boilerplate is minimal
No additional overhead compared to normal JS OOP
I realize this is an older discussion but it might still be useful to share my solution to the problem of the supposedly private variables and methods in a TypeScript "leaking" out into the public interface of the compiled JavaScript class.
To me this issue is purely cosmetic, i.e. it's all about the visual clutter when an instance variable is viewed in DevTools. My fix is to group private declarations together inside another class that is then instantiated in the main class and assigned to a private (but still publicly visible in JS) variable with a name like __ (double underscore).
Example:
class Privates {
readonly DEFAULT_MULTIPLIER = 2;
foo: number;
bar: number;
someMethod = (multiplier: number = this.DEFAULT_MULTIPLIER) => {
return multiplier * (this.foo + this.bar);
}
private _class: MyClass;
constructor(_class: MyClass) {
this._class = _class;
}
}
export class MyClass {
private __: Privates = new Privates(this);
constructor(foo: number, bar: number, baz: number) {
// assign private property values...
this.__.foo = foo;
this.__.bar = bar;
// assign public property values...
this.baz = baz;
}
baz: number;
print = () => {
console.log(`foo=${this.__.foo}, bar=${this.__.bar}`);
console.log(`someMethod returns ${this.__.someMethod()}`);
}
}
let myClass = new MyClass(1, 2, 3);
When the myClass instance is viewed in DevTools, instead of seeing all its "private" members intermixed with truly public ones (which can get very visually messy in properly refactored real-life code) you see them neatly grouped inside the collapsed __ property:
In TypeScript Private functions are only accessible inside the class. Like
And it will show an error when you try to access a private member. Here is the example:
Note: It will be fine with javascript and both function are accessible
outside.
Here's reusable approach for adding proper private properties:
/**
* Implements proper private properties.
*/
export class Private<K extends object, V> {
private propMap = new WeakMap<K, V>();
get(obj: K): V {
return this.propMap.get(obj)!;
}
set(obj: K, val: V) {
this.propMap.set(obj, val);
}
}
Let's say you have class Client somewhere that needs two private properties:
prop1: string
prop2: number
Below is how you implement it:
// our private properties:
interface ClientPrivate {
prop1: string;
prop2: number;
}
// private properties for all Client instances:
const pp = new Private<Client, ClientPrivate>();
class Client {
constructor() {
pp.set(this, {
prop1: 'hello',
prop2: 123
});
}
someMethod() {
const privateProps = pp.get(this);
const prop1 = privateProps.prop1;
const prop2 = privateProps.prop2;
}
}
And if all you need is a single private property, then it gets even simpler, because you would not need to define any ClientPrivate in that case.
Worth noting, that for the most part, class Private just offers a nicely readable signature, whereas direct use of WeakMap does not.
In Summary - The type system will throw a warning message. But the private is a type system-specific feature, so it will go away at runtime.
Read an article I wrote about accessing TypeScript private variables here: https://szaranger.medium.com/stop-relying-on-private-to-hide-variables-in-typescript-3c45d25a58d0
Actually the answer to this question is rather simple.
You have this code:
class Test{
private member: any = "private member";
}
alert(new Test().member);
In that code, you are mixing two different languages. This part is TypeScript:
class Test{
private member: any = "private member";
}
and this part is JavaScript:
alert(new Test().member);
The private keyword in the Test class for member field is for TypeScript. Thus other classes within TypeScript cannot access the member field because the TypeScript compiler will not allow it. For example, if you tried this, it will not work:
class Test2 {
constructor() {
var test = new Test();
test.member = "Cannot do this";
}
}
It makes no difference whether you put private or public on the generated JavaScript. The generated JavaScript code will always be:
var Test = (function () {
function Test() {
this.member = "private member";
}
return Test1;
}());
Therefore, you are able to do this because JavaScript will allow this:
alert(new Test().member);
This is not a rule carved in stone and there may be cases that I am not aware of but if you are using TypeScript, then why worry about what you are allowed to do using JavaScript; the idea is that you are no longer writing JavaScript so what you can/cannot do in JavaScript should not be something to worry about anymore. To me this worry would be the same as writing C# code and then saying how come I am able to change the private field in CIL or assembly language. I am not sure if CIL allows it or not, but that is not the point. The point is you just don't go poking around in what you can do with CIL after you write code in C#.
There may be cases where you write code in TypeScript but the public may use the generated JavaScript, a plugin perhaps, and you don't want them to break things, well in that case you would worry about it. For those cases, you would write your TypeScript code to make the fields private even on the JavaScript side. Other answers have already covered on how to do that.
I was trying ES6 syntax and find I cannot define prototype property or instance property within class defination, why forbids it?
I was using MyClass.prototype.prop=1 before, try ES7 by babel compiler as below, still cannot define prototype property.
class MyClass{
prop=1;
static sProp=1;
}
I don't think define instance property is any dangerous, there's 2 cases in my own browser game need prototype property:
Subclass instances need to inherit same property value from base class:
var Building=function(){...}
Building.prototype.sight=350;
TerranBuilding.CommandCenter=...(CommandCenter extends Building)
TerranBuilding.Barracks=...(Barracks extends Building)
So CommandCenter and Barracks will both have same building sight as 350.
new CommandCenter().sight===new Barracks().sight//All buildings have same sight
Buffer effect override original property and remove buffer
Marine.prototype.speed=20
var unit=new Marine()
unit.speed===20//get unit.__proto__.speed 20
unit.speed=5//Buffer:slow down speed, unit.speed will override unit.__proto__.speed
delete unit.speed//Remove buffer
unit.speed===20//true, speed restore
So I think it should add a way to set prototype property instead of forbid it completely, or can you give some other solutions to deal with above 2 cases?
Updated Answer (April, 2022)
Just two months after my previous answer, in August of 2021, the static block proposal was moved to stage 4 by the TC-39 committee. See the whole informal list of finished proposals here.
For those looking to get a use case summary of static blocks in Javascript, read the initial publication from the V8 blog from March 2021, after their implementation.
Also, see the MDN documentation for static initialization blocks.
Though most all updated browsers now support this, read below if you really like to support Internet Explorer.
Original Answer
Below is the typical pattern I follow in javascript. Native, no babel, etc..
It mirrors the static-block style that java uses. There is a Stage 3 Proposal open for this right now, and I expect therefor, that it will be standardized in the near future (as is consistent with the stage 3 proposal expectations of the TC-39 committee).
What the proposal will look like
class MyClass {
static {
// Any code here is executed directly after the initialization
// of MyClass. You can add prototype stuff here. The function
// is called bound to `MyClass`.
}
}
This can be done today using a static iife
These will function exactly the same way.
class MyClass {
// Using private properties is not required, it is just an option. Make
// sure to use an arrow function so that `this` refers to `MyClass`,
// Note that `MyClass` will still be in the functions closure.
static #_ = (() => {
// 'Almost' how functions are typically added. ES6 style
// is always recommended over this.
this.prototype.myFunc = function myFunc() {
console.log(":D");
};
// ES6 would actually do this (approximately) so that the function is
// non-enumerable in the prototype.
Reflect.defineProperty(this.prototype, "myFunc", {
// enumerable: false, // defaults 'false'
writable: true,
configurable: true,
// I'm intentionally not using the shorthand for the function
// so that it is named 'myFunc'.
value: function myFunc() {
console.log(":D");
}
});
// Note that all children of MyClass will refer to this exact
// object if put in the prototype, i.e. not a copy of it.
// Also, this property will be non-enumerable on the children
// (but enumerable on the prototype itself unless you
// use `defineProperty` as above).
this.prototype.sharedProperty = { name: "Gerald" };
})();
}
Neither of those will be on the class prototype.
The class Foo { bar = 1; } syntax will assign a value to the class instance, to be accessed with this.bar.
The class Foo { static bar = 1; } syntax will assign a value to the class constructor, to be accessed with Foo.bar.
There isn't much reason to use the prototype in this case. It will only complicate who actually owns the property and assigning a number in a few different classes will have very little overhead.
I would suggest the class instance property and just use this.sight everywhere you need it.
The simplest way to add a property to the prototype inside the class body is by using the prototype assignment as a "value" for a dummy static property:
class MyClass {
static _dummy = MyClass.prototype.prop1 = <expression1>
static _dummy = MyClass.prototype.prop2 = <expression2>
// or
static _dummy = this.prototype.prop2 = <expression2>
}
(it works without parentheses because = is right-associative, and it's fine to re-use the same dummy property for each prototype assignment)
If you want to do more interesting (multi-line) computation for the values, an initializer can be an immediately-executed function expression, in which case you've basically created a static constructor and you can put all the initializations for the prototype and class object in that.
I think the other answer didn't get the point of this question. The whole point of having inheritance is that you can decide when and where to override something. and if anyone think that's an overhead, why does ya use an OOP language at all?
I don't know why it's "forbidden" after all, but I could share some ideas.
I'm pretty sure there is no way to define a Prototype Property with 'class' keyword. Any definition will be install on "hasOwnProperty". A huge setback is that in a constructor, there is no way to have any parents' constructors to interact with an overridden property.
To the point of reasoning, it's actually expelled by an other feature: you can use expressions to assign properties to this.
class A extends B { sight = this.getSight() * 3 }
When an expression excuses, it is either run with instance - created with constructor, or run at class declaration - when the prototype is created.
Accessors and methods don't have this problem. They are defined at prototype definition time and called at instance run time.
Property defined with expression with "=" is the return value of the expression. It is excused right after definition - should be the instance creation time, otherwise this could not be available.
So it's nothing about patterns. It's about having expressions or having inheritance. I definitely prefer inheritance, expressions are so pointless when you can write them right into the constructor.
class A extends B { constructor() { this.sight = this.getSight() * 3 }
Using decorators are a nice work around. You can always do something with the prototype in javascript:
#B({sight:2}) class A {};
decorator B is:
function(option) {return function(clazz) {clazz.prototype.sight = option.sight; return clazz}}
Using Class static initialization blocks1:
class MyClass {
static {
this.prototype.prop = 1;
}
}
console.log(MyClass.prototype.prop); // 1
const instance = new MyClass();
console.log(instance.__proto__.prop); // 1
this in the static block differs as1:
The this inside a static block refers to the constructor object of the class.
The code inside the static block is executed only once when the class initialization gets evaluated.
Note: Safari doesn't support this feature as of June 2022. You can check the latest info on, for example, mdn web docs1.
[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Class_static_initialization_blocks
class MyClass {
constructor() {
MyClass.prototype.prop2 = "Marry";
}
}
const mc = new MyClass()
mc.__proto__ // { prop2: "Marry" }
What was the idea about leaving out something like this in ES6:
class Foo {
myMethod(){
// do something with 'bar'
}
constructor(){
this.myMethod();
}
otherMethod(){
this.myMethod();
}
}
I know that it's possible to define the function in the constructor or outside the class and then use it with myMethod(). However coming from other languages I was surprised to see classes, but no local (or private) methods. I couldn't find anything on the internet about the reason why this was left out.
EDIT:
I just realized your post was about functions, not variables. Since functions are a type of variable, all these solutions work for function even though I didn't explicitly make the examples functions
I have found several solutions, each of which have their pros and cons:
Method 0: Factories
var Foo = (function() {
let priv = {
"eh": 0
};
return class Foo {
constructor(num) {
priv.eh = num;
}
test() {
return priv.eh;
}
};
})();
var a = new Foo(383);
console.log(a.test());
Taking advantage of JS scoping to hide a variable, priv behind a function
Pros:
Perfectly secure. It's basically impossible to access priv unless you return a pointer of it
Takes advantage of a well-used javascript paradigm. Factories have been used by programmers for year
Private variables do not clash with parent class(es)
Cons:
It's not very clear or readable
Method 1: Define everything from the constructor
class Foo2 {
constructor(num) {
Object.assign(this, {
test() {
return num;
}
});
}
}
var b = new Foo2(262);
console.log(b.test());
Just what it says on the box.
Pros:
Perfectly secure again. There's no way to access local variable from outside the scope
Little more readable than Method 1. It's somewhat obvious what everything does
Private variables do not clash with parent class(es)
Cons:
Clogs the constructor function
Still not very readable
Method 2: Naming Convention
class Foo3 {
constructor(num) {
this._eh = num;
}
test() {
return this._eh;
}
}
var c = new Foo3(101);
console.log(c.test());
No need to hide behind strange security procedures. Just specify in the name which properties are "private"
Pros:
Very easy to read, can take advantage of class structure
Cons:
Offers absolutely no protection, only a recommendation.
Private variables clash with the private variables of parent classes
Method 3: Symbols
const eh = Symbol("eh");
class Foo4 {
constructor(num) {
this[eh] = num;
}
test() {
return this[eh];
}
}
var d = new Foo4(100);
console.log(d.test());
I just wanted to include this one because I thought it was cool
Pros:
Readable as naming convention. Private variables don't get strings, they get Symbols. Very easy to read
Cons:
Pointless. In any situation where the parent scope is protected, you can just store private variables there
Not secure. Even if you solve the problem above, people can access all keys (including Symbols) with Reflect.ownKeys()
Hope this was helpful!
I would like to set a design standard for class- as well as class-instance-creation. Combining lots of intel from multiple websites (e.g. from stackoverflow), there finally is a way to have a relative maximum of flexibility. My goal is exactly that in terms of having code-structures that behave similar to more defined classes of Java and the like.
Here is working codesnippet of what I have so far (including explanations):
var MyClass = function (prop1)
{
var _class = MyClass;
var _proto = _class.prototype;
// public member of constructed class-instance
this.prop1 = prop1;
// private static property as well as private member of class-instances
// (see getter below!)
var prop2 = this.prop1 * 10;
// need to use this. instead of _proto because the property prop2 of
// the class itself would be returned otherwise
this.getProp2 = function ()
{
return prop2;
}
// 1 function for all instances of the class
// reached by a fallback to the prototype
_proto.protoAlert = function ()
{
// must call this.getProp2() instead of using prop2 directly
// because it would use the private static member of the class
// itself instead the one of the class-instance
alert(this.prop1 + " " + this.getProp2());
}
};
var c1 = new MyClass(1);
c1.protoAlert();
var c2 = new MyClass(2);
c2.protoAlert();
c1.protoAlert();
This works well so far. However, there are some hurdles to take to not provoke errors and uncatched misbehavior of the script. The private property prop2 exists in both class and class-instances. It's a likely unintended double identity. Furthermore, the private property of class-instances are only properly reachable through setter- and getter-function. This is not the worst thing as it enforces a common way to access private variables. The downside is: Setters and getters have to be called with this. to actually reference to the prop2 of the class-instance then returning it. As for class inheritance - I didn't look into this topic with my current standard yet. Hopefully, it will work out as well.
Is there a more elegant solution or at least one that is less prone to possible errors?
Thank you in advance!
JavaScript does not really provide practical pattern for private properties. The pattern you're using does work only as long as you define all methods in constructor. You should keep in mind that this means every time you create the class, you create all the methods.
If you think about it, private variables are not serving any function in the program, they serve the programmer to keep in mind, that he should and what he should not be changing. As such, you can simply use some naming pattern. I've seen this a lot along other people's code:
function MyClass() {
// Private property
this._helloWord = "Hello word.";
}
// From outside, accessed as `helloWord`, without underscore
Object.defineProperty(MyClass.prototype, "helloWord", {
get: function() {console.log("helloWord getter");return this._helloWord;},
set: function(value) {console.log("helloWord setter");return this._helloWord = value;},
};
MyClass.prototype.alertProp = function() {
alert(this._helloWord);
}
// Accessing from the outside:
var instance = new MyClass();
alert(instance.helloWord); // will activate the getter function
Most people will instantly understand there is something special about _underscored variables. You can also make variable constant this way:
Object.defineProperty(MyClass.prototype, "helloWord", {
value: "Hello world",
writable: false // <----
};
Learn more about Object.defineProperty. You should also get to understand that the structure of Javascript is a little bit different than in OOP languages. If you try to push other languages' patterns on it, it will cause performance and structural problems.
The way I figured, when creating a new function (that represents a class), it is considered a good practice to define additional functions with the help of the prototype. If functions are declared through this within an existing function, they get created for each instance, which we don't necessarily want.
So, my question is - if I want to have a property that is completely private and can be access only through getters and setters, is it even possible to achieve this by using the prototype?
Here's an example:
function Item() {
var title = '';
this.setTitle = function(_title) {
title = _title;
};
this.getTitle = function() {
return title;
};
}
var car = new Item();
car.setTitle('car');
console.log(car.getTitle()); //car
console.log(car.title); // undefined
/*
Alternative
*/
function _Item() {
this.title = '';
}
_Item.prototype.setTitle = function(_title){
this.title = _title;
};
_Item.prototype.getTitle = function() {
return this.title;
};
var _car = new _Item();
_car.setTitle('car 2');
console.log(_car.getTitle()); // car
console.log(_car.title); // car
as can be seen from the example above, in the case of Item, I declared getters and setters within a function - not a good practice. But in this way, I managed to keep the title property private. However, in case of _Item, I'm using the prototype approach, which is preferred, but my title property is not private at all.
So, what's the best approach at creating private properties of "classes" in JavaScript?
No, if you want a private property, which by definition is a variable local to the constructor, then obviously methods which access it must also be defined within the constructor.
Many people worry about the efficiency implications of defining a method once on a prototype, versus defining it once on every instance. This might have been a valid concern ten years ago, or today in applications that are creating thousands or millions of objects. Otherwise, realistically it's not something you need to worry about.