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How to use comments in React

341.3k Views Asked by At

How can I use comments inside the render method in a React component?

I have the following component:

'use strict';
 var React = require('react'),
   Button = require('./button'),
   UnorderedList = require('./unordered-list');

class Dropdown extends React.Component{
  constructor(props) {
    super(props);
  }
  handleClick() {
    alert('I am click here');
  }

  render() {
    return (
      <div className="dropdown">
        // whenClicked is a property not an event, per se.
        <Button whenClicked={this.handleClick} className="btn-default" title={this.props.title} subTitleClassName="caret"></Button>
        <UnorderedList />
      </div>
    )
  }
}

module.exports = Dropdown;

Enter image description here

My comments are showing up in the UI.

What would be the right approach to apply single and multiple line comments inside a render method of a component?

reactjs react-native
Original Q&A
16

There are 16 best solutions below

3
On BEST ANSWER

Within the render method comments are allowed, but in order to use them within JSX, you have to wrap them in braces and use multi-line style comments.

<div className="dropdown">
    {/* whenClicked is a property not an event, per se. */}
    <Button whenClicked={this.handleClick} className="btn-default" title={this.props.title} subTitleClassName="caret"></Button>
    <UnorderedList />
</div>

You can read more about how comments work in JSX here.

2
On 
{
    // Any valid JavaScript expression
}

If you wonder why it works, it's because everything that's inside curly braces { } is a JavaScript expression.

So this is fine as well:

{ /*
         Yet another JavaScript expression
*/ }
0
On

Conditional rendering

This approach mentioned on the React docs will also work with nested /**/ comments, unlike the {/**/} approach, e.g.:

{false && <>
<div>
  Commented out.
  /* Anything goes. */
</div>
</>}

Full example:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>Hello, World!</title>
<script src="https://unpkg.com/react@17/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/[email protected]/babel.min.js"></script>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
ReactDOM.render(
  <div>
    before
    {false && <>
    <div>
      Commented out.
      /* Anything goes. */
    </div>
    <div>
      Also commented out.
      /* Anything goes. */
    </div>
    </>}
    after
  </div>
  ,
  document.getElementById('root')
);
</script>
</body>
</html>

renders just beforeafter.

Ah, just noticed, one downside of this is that linters like typescript could complain about stuff in the "comment" that is not correct.

0
On

According to React's Documentation, you can write comments in JSX like so:

One-line Comment:

<div>
  {/* Comment goes here */}
  Hello, {name}!
</div>

Multi-line Comments:

<div>
  {/* It also works 
  for multi-line comments. */}
  Hello, {name}! 
</div>
2
On

Here is another approach that allows you to use // to include comments:

return (
  <div>
    <div>
      {
        // Your comment goes in here.
      }
    </div>
    {
      // Note that comments using this style must be wrapped in curly braces!
    }
  </div>
);

The catch here is you cannot include a one-line comment using this approach. For example, this does not work:

{// your comment cannot be like this}

because the closing bracket } is considered to be part of the comment and is thus ignored, which throws an error.

3
On

JSX Comments Syntax: You can use 

{/** 
  your comment 
  in multiple lines
  for documentation 
**/}

or 

{/* 
  your comment 
  in multiple lines
*/}

for multiple lines comment. And also,

{ 
  //your comment 
}

for single line comment.

Note: The syntax: 

{ //your comment }

doesn't work. You need to type braces in new lines.

Curly braces are used to distinguish between JSX and JavaScript in a React component. Inside curly braces, we use JavaScript comment syntax.

Reference: click here

0
On

To summarize, JSX doesn't support comments, either html-like or js-like:

<div>
    /* This will be rendered as text */
    // as well as this
    <!-- While this will cause compilation failure -->
</div>

and the only way to add comments "in" JSX is actually to escape into JS and comment in there:

<div>
    {/* This won't be rendered */}
    {// just be sure that your closing bracket is out of comment
    }
</div>

if you don't want to make some nonsense like

<div style={{display:'none'}}>
    actually, there are other stupid ways to add "comments"
    but cluttering your DOM is not a good idea
</div>

Finally, if you do want to create a comment node via React, you have to go much fancier, check out this answer.

0
On

According to the official site, these are the two ways:

<div>
  {/* Comment goes here */}
  Hello, {name}!
</div>

Second example:

<div>
    {/* It also works 
    for multi-line comments. */}
    Hello, {name}! 
</div>

Here is the reference: How can I write comments in JSX?

0
On

Here are 6 ways of commenting in React:

  1. Multi-line TypeScript comment
  2. HTML Attribute comment
  3. Single line JSX comment
  4. Single-line JSX comment
  5. Multi-line JSX comment
  6. Single-line JavaScript comment
/**
 * 1. Multi-line
 * TypeScript comment
 * @constructor
 */

export const GoodQuote = observer(({model} : { model: HomeModel }) => {

    console.log(model.selectedIndex)
    return useObserver(() =>
        <div /* 2. HTML attribute comment */ onClick={() => model.toggleQuote()}>
            <p>{model.quotes[model.selectedIndex]}</p>
            {
                // 3. Single-line comment
            }
            { /* 4. True Single-line comment */}
            { /*
              5. Multi-line
              React comment
            */ }
        </div> // 6. Javascript style comment

    )
})
2
On

On the other hand, the following is a valid comment, pulled directly from a working application:

render () {
    return <DeleteResourceButton
            // Confirm
            onDelete = {this.onDelete.bind(this)}
            message = "This file will be deleted from the server."
           />
}

Apparantly, when inside the angle brackets of a JSX element, the // syntax is valid, but the {/**/} is invalid. The following breaks:

render () {
    return <DeleteResourceButton
            {/* Confirm */}
            onDelete = {this.onDelete.bind(this)}
            message = "This file will be deleted from the server."
           />
}
0
On

This is how.

Valid: 

...
render() {

  return (
    <p>
       {/* This is a comment, one line */}

       {// This is a block 
        // yoohoo
        // ...
       }

       {/* This is a block 
         yoohoo
         ...
         */
       }
    </p>
  )

}
...

Invalid:

...
render() {

  return (
    <p>
       {// This is not a comment! oops! }

       {//
        Invalid comment
       //}
    </p>
  )

}
...
0
On

To write comments in JSX markup, you have to put them inside of curly braces { }

This is because without telling React that the comments is JavaScript code, it will read every slash / as part of an HTML node.

You can find more details about comments in JSX at https://thelonecoder.dev/javascript/react-js/how-to-write-comments-in-react/

Here's how to properly add the comment you tried to write in your render method:

  render() {
    return (
      <div className="dropdown">
        {
          // whenClicked is a property not an event, per see.
        }
        <Button whenClicked={this.handleClick} className="btn-default" title={this.props.title} subTitleClassName="caret"></Button>
        <UnorderedList />
      </div>
    )
  }

Note that you have to add a single-line // comment on its own line, otherwise you will be commenting out the closing brace }

The same syntax works for multi-line /* */ comments:

{
  /* This is a multi-line
     comment! */
}
0
On 

{/*
   <Header />
   <Content />
   <MapList />
   <HelloWorld />
*/}

1
On

Besides the other answers, it's also possible to use single line comments just before and after the JSX begines or ends. Here is a complete summary:

Valid

(
  // this is a valid comment
  <div>
    ...
  </div>
  // this is also a valid comment
  /* this is also valid */
)

If we were to use comments inside the JSX rendering logic:

(
  <div>
    {/* <h1>Valid comment</h1> */}
  </div>
)

When declaring props single line comments can be used:

(
  <div
    className="content" /* valid comment */
    onClick={() => {}} // valid comment
  >
    ...
  </div>
)

Invalid

When using single line or multiline comments inside the JSX without wrapping them in { }, the comment will be rendered to the UI:

(
  <div>
    // invalid comment, renders in the UI
  </div>
)
2
On

Two ways to add comments in React Native

  1. // (double forward slash) is used to comment only a single line in React Native code, but it can only be used outside of the render block. If you want to comment in a render block where we use JSX, you need to use the second method.

  2. If you want to comment on something in JSX you need to use JavaScript comments inside of curly braces like {/* Comment here /}. It is a regular / Block comment */, but it needs to be wrapped in curly braces.

Shortcut keys for /* Block comments */:

  • Ctrl + / on Windows and Linux.

  • Cmd + / on macOS.

0
On

JavaScript comments in JSX get parsed as text and show up in your application.

You can’t just use HTML comments inside of JSX because it treats them as DOM nodes:

render() {
  return (
    <div>
      <!-- This doesn't work! -->
    </div>
  )
}

JSX comments for single line and multiline comments follows the convention

Single line comment:

{/* A JSX comment */}

Multiline comments:

{/*
  Multi
  line
  comment
*/}

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