JSX | Mastering React: An In-Depth Zero to Hero Video Series

Summary

In this React JS tutorial, the instructor introduces JSX, a syntax extension for JavaScript, which makes it easier to write React applications. They explain that while JSX resembles HTML, it must follow XML rules and be converted to JavaScript using Babel. The video covers JSX's ability to embed expressions, the importance of using camelCase for attributes and events, and the distinction between valid and invalid data types within JSX. Practical examples, such as using variables and handling boolean values correctly, are provided. The instructor also highlights common mistakes, like using 'class' instead of 'className,' and offers tips for learning JSX effectively.

Takeaways

• 📘 JSX stands for JavaScript Syntax Extension, and it's a syntax extension to JavaScript but not understood by browsers.
• ⚙️ React uses Babel to convert JSX into regular JavaScript that browsers can understand.
• 🖥️ JSX is not mandatory in React, but it's more readable and convenient for developers.
• 👩‍💻 JSX allows embedding expressions using curly braces, but it can only render strings and numbers.
• 🚫 React cannot render objects or booleans as children, which can cause errors.
• 📏 JSX requires a single parent element for rendering multiple elements, otherwise it throws an error.
• 🔧 HTML attributes in JSX must follow camelCase rules, such as 'onClick' instead of 'onclick' or 'maxLength' instead of 'maxlength'.
• 📑 In JSX, you must use 'className' instead of 'class' and 'htmlFor' instead of 'for', as these are reserved words in JavaScript.
• 🎨 Inline styles in JSX must be written as objects with properties in camelCase, and separated by commas, not semicolons.
• 🚀 JSX helps make code similar to HTML but requires adherence to React-specific syntax rules, offering both flexibility and structure.

Q & A

What does JSX stand for?

JSX stands for JavaScript Syntax Extension. It is a syntax extension to JavaScript that allows you to write HTML-like code within your JavaScript files.

Why do browsers not understand JSX directly?

Browsers only understand standard JavaScript, not JSX. JSX is a syntax extension that needs to be converted into JavaScript before it can be executed by the browser.

What is the role of Babel in React applications?

Babel is a tool used in React applications to convert JSX code into JavaScript that browsers can understand and execute.

Can React applications function without using JSX?

Yes, React applications can work without JSX. You can use the `createElement` function from React to create DOM elements, but JSX is more convenient and makes the code more readable.

What is the difference between JSX and HTML?

JSX looks similar to HTML but follows XML rules, requires proper closing of tags, and must return a single parent element. Also, attributes and event references in JSX should be written in camelCase.

How can you include dynamic content in JSX?

You can include dynamic content in JSX by wrapping variables or expressions in single curly braces. For example, `{variableName}` or `{expression}`.

What types of data can be displayed directly in JSX?

JSX can directly display strings and numbers. Other data types like booleans, arrays, and objects need to be converted to strings or handled differently to be displayed.

Why should you use camelCase for attributes and event references in JSX?

You should use camelCase for attributes and event references in JSX because it is a requirement of the JSX syntax, and it ensures compatibility with JavaScript, which is case-sensitive.

What is the correct way to add a placeholder attribute to an input element in JSX?

You should use the attribute `placeholder` with the value enclosed in quotes, like `placeholder="Your text here"`.

How should you handle inline styles in JSX?

For inline styles in JSX, you should use an object instead of a string. The object properties should be in camelCase and separated by commas, not semicolons.

What is the purpose of using fragments in JSX?

Fragments are used in JSX to group multiple elements without adding an extra parent element in the DOM, which can improve readability and maintain the structure of the document.

Outlines

00:00

🎓 Introduction to JSX in React

This paragraph introduces JSX (JavaScript Syntax Extension) as a fundamental concept in React for beginners. It explains that JSX is not HTML but a syntax extension to JavaScript that allows developers to write HTML-like code in React. The paragraph clarifies that browsers do not understand JSX directly, and thus React uses Babel to convert JSX into JavaScript that browsers can interpret. The video demonstrates how JSX tags are transformed by Babel and how JSX can be used to render elements in React without being strictly necessary. It also shows how to use variables and expressions within JSX, with a focus on the limitations of displaying only strings and numbers directly. The importance of readability and the similarity of JSX to HTML is emphasized, making it a convenient tool for developers.

05:01

🛠 JSX Rules and Best Practices

The second paragraph delves into the rules and best practices for using JSX in React applications. It highlights the requirement for JSX to follow XML rules, such as proper closing of tags and the necessity of a single parent element for all JSX elements. The paragraph also addresses the use of camelCase for HTML attributes and event references within JSX, providing examples of correct and incorrect usage. It discusses the proper handling of boolean and string values in JSX attributes, the use of className instead of class, and the substitution of 'for' with 'htmlFor' due to JavaScript's reserved keywords. The paragraph concludes with a discussion on the correct way to apply inline styles in JSX, emphasizing the use of objects over strings and the importance of camelCase for property names. The speaker encourages practice and offers the suggestion to use online tools for JSX syntax conversion when needed.

Keywords

💡JSX

JSX stands for JavaScript XML, which is a syntax extension for JavaScript. It allows developers to write code that looks like HTML but is actually being converted into JavaScript objects by a tool called Babel. In the context of the video, JSX is central to the discussion as it is used to describe how React components are structured and rendered. The script mentions that 'JSX is not required for rendering contents in React' but is convenient for developers because it resembles HTML, making it easier to write and understand.

💡Babel

Babel is a tool used in the React ecosystem for converting JSX into vanilla JavaScript that browsers can understand. It plays a crucial role in the development process as it bridges the gap between the modern JavaScript features used in React and the older JavaScript that browsers can execute. The video script illustrates this by showing how Babel converts JSX tags into JavaScript objects.

💡createElement

In React, `createElement` is a function used to create React elements typically used in the render method. The video script explains that instead of returning JSX directly, developers can use `createElement` to manually create DOM elements, which can then be used in the render method. This function is part of the React API and is an alternative to JSX for creating React elements.

💡CamelCase

CamelCase is a naming convention used in programming where the first letter of each word except the first is capitalized. In the context of JSX, all HTML attributes and event references must be written in camelCase. The video script provides examples such as 'autofocus' and 'onMouseOver', contrasting them with their incorrect lowercase counterparts, to emphasize the importance of following this convention for proper attribute and event naming in JSX.

💡Fragments

In React, fragments are a way to group a list of children without adding extra nodes to the DOM. The script mentions using fragments as a better alternative to a 'div' for grouping multiple JSX elements when they don't have a clear single parent element. This helps in maintaining a clean and semantic structure in the React component.

💡Curly Braces

Curly braces in JSX are used to embed JavaScript expressions within the JSX code. The video script demonstrates how to use curly braces to insert variables or evaluate expressions within JSX elements. For instance, it shows how to wrap a variable inside single curly braces to display its value in the browser, which is a fundamental aspect of dynamically rendering content in React components.

💡Reserved Keywords

Reserved keywords in JavaScript are words that have special meaning and cannot be used as identifiers or variable names. The video script points out that 'class' and 'for' are reserved keywords, and thus, in JSX, 'className' and 'htmlFor' must be used instead. This is important for avoiding syntax errors and ensuring that JSX is correctly transpiled into JavaScript.

💡Inline Styles

Inline styles in React are used to apply CSS styles directly to elements. The video script explains that when using inline styles in JSX, developers must use an object instead of a string. It also highlights the use of double curly braces and camelCase for property names, as seen when trying to apply a style to an element, which is a key difference from HTML.

💡Boolean Attributes

Boolean attributes in HTML and JSX are attributes that do not require a value; their presence or absence indicates a true or false value. The video script discusses how boolean attributes should be passed as boolean values in JSX, using 'true' or 'false' without quotes, to ensure that the React component behaves as expected, as opposed to passing them as strings which can lead to unintended results.

💡XML Rules

JSX follows XML rules, which means that all tags must be properly closed, similar to HTML. The video script emphasizes this by stating that JSX must return a single parent element, or it won't compile, which is a direct consequence of adhering to XML's strict syntax requirements for well-formed documents.

Highlights

JSX is a syntax extension to JavaScript, allowing HTML-like structure in React components.

Browsers do not understand JSX; it is converted to JavaScript using Babel.

React can work without JSX by using the createElement function.

JSX provides a more readable and convenient way to write React components compared to JavaScript.

Variables and expressions can be embedded within JSX using curly braces.

Only strings and numbers can be directly displayed in JSX; other data types require conversion.

JSX must follow XML rules, including proper closing of tags.

A single parent element is required for JSX to compile correctly.

Fragments can be used to group multiple JSX elements without adding extra DOM elements.

All HTML attributes and event references in JSX should be in camelCase.

Reserved JavaScript keywords like 'class' and 'for' should be replaced with 'className' and 'htmlFor' in JSX.

Inline styles in JSX must be provided as objects, not strings.

Boolean attributes in JSX should be wrapped in curly braces to ensure proper evaluation.

JSX is designed to be similar to HTML, making it easier for developers to work with React.

Babel can be used to convert JSX to JavaScript, allowing developers to see the underlying JavaScript code.

It's recommended to use JSX syntax conversion tools only when stuck, to encourage learning and understanding of JSX.

The tutorial suggests practicing with JSX by creating a React application and experimenting with different elements.

Transcripts

Hi Friends

Welcome back to React JS - Zero to Hero series.

This series is for beginners who wants to learn React JS from Scratch.

In the last video I have explained about the file structure in react application and how

a react application is actually working and in this video I am going to explain about

JSX.

Let's start.

In the last video, I have explained that this function is returning a JSX and we are showing

that inside the root div element.

This appears to be a html h1 element.

But actually it is not a html element.

This is a JSX element.

So, what is JSX?

JSX means Javascript Syntax Extension.

It is a syntax extension to Javascript.

But browsers does not understand JSX.

They understand Javascript only.

So, react is using a tool called Babel, which is responsible for converting this JSX into

Javascript.

For example, here we have a JSX tag.

Babel converts this to something like this.

So, instead of returning a JSX in a function and using that function in render method,

I can use the createElement function from React to create my DOM element.

And I can use that element inside render method.

And so we can see our new heading is showing up.

So, actually JSX is not required for rendering contents in react.

React works without JSX also.

But it is convenient to use JSX.

Let me explain.

First let me go to a website, in which we have the Babel tool which converts JSX into

Javascript.

So here, let me type a simple JSX code, and in the right hand side, we can see how Babel

converts this code.

Let me type one complex JSX where we have nested elements.

This is getting converted to this.

In the first look, it appears to be created so many elements, but you can see some of

them are nested.

If I prettify this, we can understand.

So, comparing to this, this one is more readable and easy for developers to develop because

this is almost same as HTML.

That is the reason we are using JSX in react.

Ok.

Let's explore more on JSX.

Let me use this function instead of this element we created.

And here, instead of hardcoding the text, let me assign it to a variable.

Now, I need to use this variable here.

I can do this by wrapping the variable inside single curly braces, like this.

So, we can see that in the browser.

If I change the value of this variable, we can see it is getting updated.

Not only this, I can also evaluate an expression inside this.

But we need to understand that, this can display only string and numbers.

Let me show that.

Right now, this is showing a string.

Let me change it to a number.

And so, we can see that also.

Let me try the other data types.

I am going to use a boolean.

Now, it is not displaying the boolean.

Let me try an array.

Now, we can see it is concatenating all the items inside the array and displaying that.

This is not the result we are expecting, because when we have a boolean inside array it is

going to skip that.

Let me also try with an object.

Now, it is not showing anything.

That is because, it is throwing error.

If I open the console, we can see that.

Objects are not valid as a React child.

So, we need to keep in mind that we can show only strings and numbers.

Or, we can have a function which returns strings or numbers.

But, while using a function, we need to make sure that we are calling that function.

If we miss this parenthesis, we get the same kind of error.

Functions are not valid as a React child.

Ok.

JSX looks similar to HTML.

But we need to follow certain rules in JSX.

For example, JSX follows XML rules, and therefore HTML elements must be properly closed.

One of the major differences between HTML and JSX is that in JSX, you must return a

single parent element, or it won't compile.

For example, here we are rendering a h1 element.

Now we need to render a h2 element after this.

And so, let me add that.

Now, we can see it is having an error.

If I mouse over, we can see it is complaining, JSX elements must have one parent element.

So, I need to wrap these two heading tags inside a parent tag.

Like this.

And so, it is working.

But, instead of div, we can use fragments.

Like this or like this.

Fragments are better than div.

For better readability, we can keep each element in each line.

And, we can wrap this inside a parenthesis.

Like this.

Next, we need to write all HTML attributes and event references in camelCase.

Let me create an input element.

And let me add maxlength attribute to that.

We can see it is working.

But if I inspect, we can see a warning in console.

It is suggesting to use camel case.

Ok.

Let me try with another attribute, autofocus.

This time, we can see it is giving us warning, in the mean time it is also not working.

Let me change it to camelCase.

Now, we can see, that error is gone and it is working.

So, regardless of whether it is going to work or not, we shall always use camel case for

attributes.

Not only for attributes.

We need to use camel case for events also.

So, instead of onclick, we need to use onClick.

Instead of onmouseover, we need to use onMouseOver and so on.

Ok.

A question to you.

I want to add a placeholder message to this input box, so what should I do?

Do I need to use this placeholder or this placeHolder?

Actually, we need to use the first one, because in english placeholder is a single word.

Also, we are using quotes for values.

For max length, we have mentioned as 5 and we are seeing it is working.

Similarly, for auto focus, we can give true.

We can see, it is working.

But we are seeing a warning that we are passing a string instead of boolean.

That is because, let me change this true to false and so I am expecting the text box should

not be focused.

But unfortunately, it is still getting focused, because string of false is actually converted

as boolean true.

That is why, for attribute values, we need to use curly braces in JSX.

Let me change them.

Now, we can see, there is no error and input box is also not focused.

Let me change it to true.

Now, it is working as expected.

Ok, and for some attributes, we have JSX alternatives.

For example, let me add a class attribute to this h2 element.

Now, we can see JSX is complaining that we cannot use class, instead we need to use className,

because class is a reserved keyword in JavaScript.

So, let me change that.

Similarly, assume I have a label, for this input element.

Now, we can see, it is complaining, because for is also a reserved keyword in Javascript.

So, here instead of for, we need to use htmlFor.

Like this.

Now, we can see it is working.

And the last rule is, if we need to use inline styles, we need to use object instead of string.

First let me try with string.

We can see, the editor itself complaining about the error.

In case, if I save, we can see similar kind of error in the console also.

So, let me change that to object.

Now you can notice double curly brace here.

But still it is throwing some error.

That is because, we need to separate properties with comma instead of semicolon.

And, one last thing is we need to specify the properties also in camelCase.

Now it is working.

So, I believe you got some idea about JSX.

At first, you may feel some discomfort with JSX.

Often you may use class instead of className.

But you will be familiar when you start working in React.

Also, if you stuck on some JSX syntax, you can make use of websites like this, where

you can type HTML code and it will give you the JSX syntax.

But I suggest you to use these kind of sites only when you are stuck.

And, for this topic I don't want to give any assignment or task.

But you can try creating a react application and play around with some JSX elements.

Ok.

That's all for today.

Please like this video.

Subscribe my channel and support me.

Thank you.

Bye.