Why are stateless functions not supposed to have methods?

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I have read in multiple places that stateless functions in React are not supposed to have inner functions. Why is it so, though it works?

const Foo = () => {
 let bar = () => {
    return <span>lorem ipsum</span>
 return <div>{bar()}</div>

This works. But, why is this not supposed to be done?

N.B. This answer assumes that the use of the word "method" was incorrect, and that we are actually talking about an inner function, as in the example provided in the question.

A stateless component is defined as a function which returns something that can be rendered by React:

const MyStatelessComponent = function (props) {
  // do whatever you want here

  return something; // something must be render-able by React

To (re-)render the component, React calls the function, so it makes sense to perform expensive computations in advance and save their result outside of the function.

In your toy example, the function bar is declared once per render, and only used once. Let's assume that it was slightly more complicated and pass it a single parameter:

const Foo = () => {
  let bar = text => {
    return <span>{text}</span>
  return <div>{bar("lorem ipsum")}</div>

By moving bar outside of the component, you don't need to create the function once per render, you just call the function that already exists:

const bar = text => {
  return <span>{text}</span>

const Foo = () => {     
  return <div>{bar("lorem ipsum")}</div>

Now your component is ever-so-slightly more efficient, since is does less work every time it is called.

Also note that bar is almost the same as a stateless component now, and could easily be turned into one by making the function take a props object rather than a single string argument.

But the bottom line is that you can do whatever you want inside the stateless component. It just is worth bearing in mind that it will happen once per (re-)render.

Stateless Component vs Pure Component, twice you will always have exactly the same result. This is a patter you usually find in functional programming languages where you don't have methods depending on an instance and the corresponding instance variables. If stateful, here's what the state of an object should expose: Make entity classes stateful. Helper / Operation classes should be stateless. Make sure the Helper classes are not static. Even if there is a hybrid class, make sure it's not violating the SRP. Spend some time on the class design before coding.

While still valid code, as far as react is concerned, the above example is not a stateless component.

A stateless component is basically a shortcut to the render method of a stateful component (without the same life-cycle) and should "ideally" only return data, not define methods or actually manipulate or create additional data or functionality. With a stateful component, ideally, you do not define methods within the render method so none should be added in a stateless component.

By defining a method, function, or parameter inside of a stateless component but outside of the render method, you are essentially saying that there is a possibility of manipulation within the stateless component, which defeats the purpose.

Mind you, it's still valid code...but just not "react" ideal.

What is stateless programming and what are some examples?, I have read in multiple places that stateless functions in React are not supposed to have inner functions. Why is it so, though it works? const Foo = () => { let bar  Why use it, you might ask ? Stateless functional components are simpler. No members, no state, no lifecycle hooks, no multiple moving parts. This means they're simpler to understand and less prone to bugs. They're more predictable and simpler to test . Stateless functional components take the paradigm 'props in' => 'VDOM out' to it's finest level.

The function Foo is basically the render method of the React component. Therefore, it will be called everytime the component needs to be rendered. By declaring a local function inside it, it will create a new function everytime the component re-renders, which is bad. Either declare the function outside or implement a stateful component instead.

React Functional or Class Components: Everything you need to , When I said that it should return a react element it might not have been clear for you. function returns and what returns the stateless component function function), a class component has state, lifecycle methods and React  For all these reasons, we should strive to use stateless functional components wherever possible. Stateless components are just the latest reason why I love teaching React. React stateless functions offer the most elegant approach I’ve seen for creating a reusable component in any popular framework. Yes, even including Angular 2.

React: Class Component vs Functional Component, Is there any way to test methods inside stateless components? but just curious to know if there's any way to test those functions? What I meant was: we SHOULD NOT be using stateless functional components if we have  Even with all of this in mind, you can plainly see that doing a POST issuance in a stateless manner means that you do not have to wait for server synchronization to ensure the process has been properly completed, as you would with FTP or other stateful services.

Why are stateless functions not supposed to have methods , STATELESS COMPONENT declared as a function that has no state and returns have backing instances, and do not have the component lifecycle methods. Suppose you creating a dictionary page in which you display the  I like implementing service classes as stateless. However, I also like to decompose my logic into more, simple methods or functions. In some scenarios it seems like the two are somewhat against each other. Consider the following two examples. I have an entity object called House, implemented something like this.

instance() on stateless components · Issue #666 · enzymejs/enzyme , These components must not retain internal state, do not have backing instances, and do not have the component lifecycle methods. They are  tion for a traditional design). Of course, the stateless net-work functions approach may not be suitable for all net-work functions, and there are further optimizations we can make to increase processing rates. This work, how-ever, demonstrates that there is value for the functions we studied and that even with our current prototype, we are

  • I dont see a method?
  • a) that's not a method, that's a local function b) there's no advantage of having the bar as an inner function here
  • Nope. bar is not associated to Foo
  • If you would do Foo.bar = () => ...; then bar would be a method of Foo as there is a direct relationship between them. (And there are no dumb questions, just dumb answers, I'm here to help :))
  • Methods are similar to Functions in that they both are... functions. However, they differ in that Methods are a property of an object. bar() here is not a method because you cannot do Foo.bar() and also because this doesn't make sense inside Foo.
  • This is still considered a stateless component. Stateless components don't have to be considered immutable with their prop data, they just simply don't have access to the React lifecycle.
  • While this is technically correct, it doesn't answer the question in any way.
  • By declaring a local function inside it, it will create a new function everytime the component re-renders, which is bad. not really. It (maybe) creates a new closure, but im not sure why that should be bad...
  • It's not necessarily "bad" it's just pointless to create a new function multiple times if it always does exactly the same thing and will only ever be called once.