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React Tips — Infinite Scroll, Submit, Focus, and Drag and Drop

aumayeung profile image John Au-Yeung Originally published at thewebdev.info ・3 min read

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React is a popular library for creating web apps and mobile apps.

In this article, we’ll look at some tips for writing better React apps.

onSubmit in React

To run a submit handler in a React app, we should call preventDefault to prevent the default submit behavior, which is to submit to a server.

For instance, we write:

class App extends React.Component {

  submit(e){
    e.preventDefault();
    alert('submitted');
  }

  render() {
    return (
      <form onSubmit={this.submit}>
        <button type='submit'>click me</button>
      </form>
    );
  }
});
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We called e.preventDefault() with the submit method, which we pass as the value of the onSubmit prop.

React onClick Being Called on Render

We’ve to pass in the reference to a function instead of calling it.

For instance, we write:

class Create extends Component {
  constructor(props) {
    super(props);
  }

  render() {
    const playlist = this.renderPlaylists(this.props.playlists);
    return (
      <div>
        {playlist}
      </div>
    )
  }

  renderPlaylists(playlists) {
    const activatePlaylist = this.activatePlaylist.bind(this, playlist.id);
    return playlists.map(playlist => {
      return (
        <div key={playlist.id} onClick{activatePlaylist}>
          {playlist.name}
        </div>
      );
    })
}
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We have:

this.activatePlaylist.bind(this, playlist.id)
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which returns a function that changes the value of this to the current component.

Also, it passes the playlist.id as the argument to the this.activatePlaylist method.

Making React Component or Element Draggable

To create a draggable component easily, listen to the mousemove, mousedown, and mouseup events

For instance, we can write:

import React, { useRef, useState, useEffect } from 'react'

const styles = {
  width: "200px",
  height: "200px",
  background: "green",
  display: "flex",
  justifyContent: "center",
  alignItems: "center"
}

const DraggableComponent = () => {
  const [pressed, setPressed] = useState(false)
  const [position, setPosition] = useState({x: 0, y: 0})
  const ref = useRef()

  useEffect(() => {
    if (ref.current) {
      ref.current.style.transform = `translate(${position.x}px, ${position.y}px)`
    }
  }, [position])

  const onMouseMove = (event) => {
    if (pressed) {
      setPosition({
        x: position.x + event.movementX,
        y: position.y + event.movementY
      })
    }
  }

  return (
    <div
      ref={ref}
      style={styles}
      onMouseMove={ onMouseMove }
      onMouseDown={() => setPressed(true)}
      onMouseUp={() => setPressed(false)}>
      <p>drag me</p>
    </div>
  )
}
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We have the Draggable component with some props.

We listen to the mousedown and mouseup events to set the pressed state to be false and true respectively.

This will let us dragged if the pressed state is true , which is when we’re dragging.

Then we add a listener for the mousemove event by passing the onMouseMove function to the onMouseMove prop.

Then we set the position in the onMouseMove function.

We set the position by changing the x and y coordinates of the div if pressed is true .

Infinite Scrolling with React

To add infinite scrolling easily with React, we can use the react-infinite-scroller package.

To install it, we run:

npm install react-infinite-scroller
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Then we can use it by writing:

import React, { Component } from 'react';
import InfiniteScroll from 'react-infinite-scroller';

class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      listData: [],
      hasMoreItems: true,
      nextHref: null
    };
    this.fetchData = this.fetchData.bind(this);
  }

  async fetchData(){
    const listData  = await getJobsData();
    this.setState({ listData });
  }

  componentDidMount() {
     this.fetchData();
  }

  render() {
    const loader = <div className="loader">Loading ...</div>;
    const JobItems = this.state.listData.map(job => {
      return (<div>{job.name}</div>);
    });
    return (
      <div className="Jobs">
         <h2>Jobs List</h2>
         <InfiniteScroll
           pageStart={0}
           loadMore={this.fetchData.bind(this)}
           hasMore={this.state.hasMoreItems}
           loader={loader}
         >
            {JobItems}
         </InfiniteScroll>
      </div>
    );
  }
}
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We use the InfiniteScroll component to add infinite scrolling to our app.

pageStart is the starting page number.

loadMore is the function to load more data.

hasMore is the state to see if we have more data.

loader is the loader component.

We get new data every time we load and scroll to the bottom of the page.

Select All Text in Input with React When it’s Focused

We can call the select method on the input to focus it.

For instance, we can write:

const Input = (props) => {
  const handleFocus = (event) => event.target.select();

  return <input type="text" value="something" onFocus={handleFocus} />
}
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We have the handleFocus function that calls the select method on the input element to select the input value when it’s focused.

With a class component, we can write:

class Input extends React.Component {
  constructor(){
    super();
    this.handleFocus = this.handleFocus.bind(this);
  }

  handleFocus(event){
    event.target.select();
  }

  render() {
    return (
      <input type="text" value="something" onFocus={this.handleFocus} />
        );
    }
}
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We have the handleFocus method to call select to select the input value when we focus the input.

Conclusion

We can use a package to add infinite scrolling easily.

Also, we can select the values of the input.

We can add a draggable item to our component without a library.

We’ve to call preventDefault to stop the default submit behavior.

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