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React Props complete guide for beginners

SUCHINTAN DAS on June 25, 2022

Table of Content 📌 Introduction 📌 React Props 📌 Pro Tips ➡ Reduce JSX Redundancy ➡ Communicate between Parent and Child ➡ Trian...
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peerreynders profile image
peerreynders • • Edited

It's very similar to inheritance where some properties are passed from parent to child.

Inheritance is a is-a relationship. The relationship between a container and nested component is a has-a relationship.

Early React even described it as the owner-ownee relationship but community usage moved towards "parent-child" even though that makes absolutely no sense in reference to props.children.

function Avatar({username}) {
  return (
    <div>
      <ProfilePic username={username} />
      <ProfileLink username={username} />
    </div>
  );
}
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Old usage:

  • Owner: Avatar
  • Ownees: div, ProfilePic, ProfileLink
  • div is the parent to ProfilePic, ProfileLink
  • ProfilePic, ProfileLink are children to div

Community Usage:

  • Parent: Avatar
  • Child: div, ProfilePic, ProfileLink
  • div is the parent to ProfilePic, ProfileLink
  • ProfilePic, ProfileLink are children to div

Note how the community usage makes matters a lot more confusing.

  • Avatar is the Parent to div, ProfilePic, ProfileLink
  • ProfilePic, ProfileLink are passed via props.children to div

Two entirely different sets of parent-child relationships for everyone. And worse div has very little "parental control" over props.children short of ignoring them which is largely what happens in user components even though props.children is React's equivalent to WC's unnamed slot.

You use

<Children childcard={card("Child")} />
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What's wrong with using props.children instead:

<Children>
  <Card title="Child"/>
<Children/>
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which preserves the familiarity with markup better?

you can actually send HTML to your child like any card body

There is no actual HTML or even DOM involved; that is all react-dom's job'. JSX is a DSL for representing the React component tree where each component instance is responsible for rendering ReactNodes.

"JSX is an XML-like syntax extension to ECMAScript without any defined semantics."
JSX specification

JSX doesn't follow HTML formatting rules but stricter XML rules and is a JavaScript extension that in some framework specific way compiles to some JavaScript code that will eventually lead to some DOM elements being manipulated/created.

In the case of React the component tree is assembled; in the case of SolidJS actual DOM nodes are created to be included in the page's DOM - no HTML.

JSX's representation evokes the familiarity of markup—but it isn't markup.

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naveennamani profile image
naveennamani •

I'm about to comment on that HTML part. JSX is just a representation of virtual DOM using HTML like syntax, however all the JavaScript code is generated by tools like Babel.

You can play around online Babel compiler and see for yourself how your JSX turns into js code which is what is handled by react.

https://babeljs.io/repl/#?browsers=defaults%2C%20not%20ie%2011%2C%20not%20ie_mob%2011&build=&builtIns=false&corejs=3.21&spec=false&loose=false&code_lz=DYUwLgBAHhC8A8ATAlgNwHwAsTGAewgHc8AnYReAehQyA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=env%2Creact%2Cstage-2&prettier=false&targets=&version=7.18.5&externalPlugins=&assumptions=%7B%7D

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suchintan profile image
SUCHINTAN DAS •

Thanks naveennamani, for providing the link and the information.

Yes, I was also familiar with the fact that JSX is actually an extension provided by React to help us write the same code in HTML and in the backdoor it changes all the stuffs to JavaScript . Making the whole process less tiring for the developers .

But I avoided to dig that deep into the inner functionality while explaining the stuff so that any beginner can also easily grab the tip without striking their head over the whole backdoor mechanism.

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peerreynders profile image
peerreynders •

React to help us write the same code in HTML

As another commenter already pointed out to you:

  • JSX represents React Components, not HTML.

Forget about the other details with regards to JSX. However referring to JSX as HTML is problematic especially in "teaching mode" as it perpetuates the wrong mental model.

JSX lets you declaratively compose React components. That's all there is to it.

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suchintan profile image
SUCHINTAN DAS •

Peerreynders, I think you haven't read the whole sentence that I had written. I would request you to please read the whole thing as communication gap does create a lot of confusions.

In the whole line I said "JSX is actually an extension provided by React to help us write the same code in HTML and in the backdoor it changes all the stuffs to JavaScript" . I am not referring JSX as HTML, I pointed out the fact here that JSX is an extension that is provided by React to help developers write the same format of code as HTML into JavaScript with minimal changes.

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peerreynders profile image
peerreynders • • Edited

I may understand what you mean but I'm convinced that your target audience is not going to come away with the same understanding.

write the same format of code as HTML

That phrasing alone is enough to establish a false equivalence between JSX and HTML. And to some degree it's only valid as long as you are talking about React's DOM element components. User components compose those DOM components. Container components may only compose User components without adding any additional DOM components. Providers have no equivalence in the DOM at all.

JSX is what makes React declarative. HTML happens to be declarative. JSX is XML. Both XML and HTML derived from SGML.

  • JSX composes React Components
  • HTML composes markup from HTML elements

The fact that a component's position in the component tree is linked to the position of the rendered content in the DOM tree is a leaky abstraction.

React's entire premise is to reuse React components in React Native. React Native is all components and JSX; no HTML, no DOM;

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suchintan profile image
SUCHINTAN DAS •

Thanks peerreynders for the feedback. Yes, there a case that people take away a wrong concept by misunderstanding this line. I will edit this line on the blog so that atleast no misconception is spread.

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suchintan profile image
SUCHINTAN DAS •

Thanks peerreynders, for writing this much. It's really a huge chunk of information that you shared and I really appreciate your hard work and efforts.

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brense profile image
Rense Bakker •

In your first example, the const card is not HTML, it's a React component, nested inside your Parent. It's not recommended to have nested component definitions and if you absolutely feel that you must do this, you should atleast wrap it inside a useCallback hook to prevent excessive rerenders.

// Very bad for performance:
function Parent(){
  const child = () => <span>this is bad</span>
  return <div>{child()}</div>
}
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// useCallback to solve excessive rerenders:
function Parent(){
  const child = useCallback(() => <span>slightly better</span>, [])
  return <div>{child()}</div>
}
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// Just define as its own component:
function Child(){
  return <span>I'm a child!</span>
}

function Parent(){
  return <div><Child /></div>
}
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suchintan profile image
SUCHINTAN DAS •

Thanks Rense , for the sharing the amazing tip. While I was writing that pro tip my idea was to illustrate that we can send a HTML code also as props to our child component to render.

Yes, while taking the example I tried to keep it short , resulting in a bit unclear manner about why to use it.

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brense profile image
Rense Bakker •

Oh and your darkMode / lightMode definitions seem like a lot of duplication of code... Why not just do something like this?:

function ToggleButton(props){
  return <i
    className={`fa-solid ${props.icon} ${props.isActive ? 'toogle-active' : 'toogle-inactive'}`}
    onClick={tooglemode}
  />
}

function Toggle(){
  return <div className="toogle">
    <ToggleButton isActive={!dark} icon="fa-moon">
    <ToggleButton isActive={dark} icon="fa-sun">
  </div>
}
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suchintan profile image
SUCHINTAN DAS •

Right Rense, this would be a better approach to implement that feature. I haven't really thought about implementing it in that manner.

Really appreciate you efforts for sharing this amazing approach with the community 🙂.

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suchintan profile image
SUCHINTAN DAS •

Guys if you want me to cover any topic 💭 , you can comment here . I assure you that I maintain a good list of such topics and will surely cover them soon.

I always believe in sharing valuable knowledge with my connections. And if I can share knowledge about a needy topic , it's a pleasure for me .

Do comment below 👇!

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ivadyhabimana profile image
Ivad Yves HABIMANA •

React hooks

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suchintan profile image
SUCHINTAN DAS •

Sure Ivad, I will cover all the hooks in React over one blog in a broad way. Stay tuned !