With one simple swipe of the cursor, you can select a word, passage, or paragraph to highlight it.

As you see above, in this article, we'll build the Medium Highlights tool using React Hooks.

Table of content

• Pre-requirements
• Initializing your React App
• Folder structure
• Features
• Defining states
• Selecting text
• Final code

Pre-requirements

Dependency	Version
create-react-app	4.0.1+
React.js	17.0.1+
React DOM	17.0.1+
React Scripts	4.0.1+

Initializing your React App

npx create-react-app quoteh

Feel free to give a name to the app

cd quoteh

Folder structure

src
├── App.js
├── assets
│   ├── Logo.svg
│   └── Skeleton.svg
├── components
│   ├── quote.css
│   └── quote.js
├── global.css
├── index.js
├── reportWebVitals.js
└── setupTests.js

Features

Note: This repository will contain the first part of the project available for making the learning process faster and better.

The app will focus on the following features:

• Select text
  • Show popup
• Highlight selected quote
  • Share
  • Create a dynamic image (canvas)

Defining states

First of all, I always start thinking about what are the required statement variables. Basically, we have:

• X (horizontal selection: number)
• Y (vertical selection → lines: number)
• Selected text (highlighted words: string)
• Popover (open/hide: boolean)

 // Selection range initial state: number
const [xRange, setXRange] = useState(0);
const [yRange, setYRange] = useState(0);
// Selected text initial state: string
const [selectedText, setSelectedText] = useState('');
// Popover initial state: false
const [showPopover, setShowPopover] = useState(false);

Besides the statement variables, we also need to see that it is necessary to access the selected text (current value). For this, useRef will help.

const selectedTextRef = useRef(null);

Selecting text

Now, using getSelection API, you are able to access the range of the selected text. Besides that, it's necessary to convert it to a string (using toString) and remove ( trim) the new lines, tabs, etc.

const selection = window.getSelection();
const selectedText = selection.toString().trim();

We also need to create conditions: If the text was selected, show the popover. Otherwise, hide the popover.

if (!selectedText) {
  // Hide popover when the text is not selected¹
  hidePopover();

  return;
}

Before, to continue the conditions, it's necessary to get the:

• Initial selection range (getRangeAt(0))
• Start position of a node (startContainer)
• Final position of a node (endContainer)
• Current selected text (current)
• Highlightable region (querySelector)

const selectionRange = selection.getRangeAt(0);

const startNode = selectionRange.startContainer.parentNode;
const endNode = selectionRange.endContainer.parentNode;

const highlightable = selectedTextRef.current;
const highlightableRegion = highlightable.querySelector('.popover');

If the highlightable region doesn't contain a starting/final node, hide the popover.

if (highlightableRegion) {
  if (
    !highlightableRegion.contains(startNode) ||
    !highlightableRegion.contains(endNode)
  ) {
    // Hide popover when the text is not selected¹
    hidePopover();

    return;
  }
} else if (
  !highlightable.contains(startNode) ||
  !highlightable.contains(endNode)
) {
  // Hide popover when the text is not selected¹
  hidePopover();

  return;
}

We also need to get the size of the element relative to the DOM. If the width is equal to 0, hide the popover.

const { x, y, width } = selectionRange.getBoundingClientRect();
if (!width) {
  // `width` is equal to 0
  // Hide popover when the text is not selected¹
  hidePopover();

  return;
}

To finish, set the value to the respective statement variables:

• Both (x & y) ranges will be relative to the DOM
• The text will be selected (string)
• The popover will be visible (true)

setXRange(x + width / 10);
setYRange(y + window.scrollY - 34);
setSelectedText(selectedText);
setShowPopover(true);

const { onHighlightPop = () => {} } = props;
onHighlightPop(selectedText);

To capture the event, it's necessary to watch it (addEventListener) and clean after done → side effects (removeEventListener)

useEffect(() => {
  window.addEventListener('mouseup', onSelectText);

  return () => window.removeEventListener('mouseup', onSelectText);
}, [])

Final code

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