DataList

30秒学会常用React代码 (30 seconds of React - Curated collection of useful React snippets that you can understand in 30 seconds or less.)

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30 seconds of React

Curated collection of useful React snippets that you can understand in 30 seconds or less.

  • Use Ctrl + F or command + F to search for a snippet.
  • Contributions welcome, please read the contribution guide.
  • Snippets are written in React 16.8+, using hooks.

Prerequisites

To import a snippet into your project, you must import React and copy-paste the component's JavaScript code like this:

import React from 'react';

function MyComponent(props) {
  /* ... */
}

If there is any CSS related to your component, copy-paste it to a new file with the same name and the appropriate extension, then import it like this:

import './MyComponent.css';

To render your component, make sure there is a node with and id of "root" present in your element (preferrably a <div>) and that you have imported ReactDOM, like this:

import ReactDOM from 'react-dom';

Table of Contents

Array

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Input

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Object

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String

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Visual

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Array

DataList

Renders a list of elements from an array of primitives.

  • Use the value of the isOrdered prop to conditionally render a <ol> or <ul> list.
  • Use Array.prototype.map to render every item in data as a <li> element, give it a key produced from the concatenation of the its index and value.
  • Omit the isOrdered prop to render a <ul> list by default.
function DataList({ isOrdered, data }) {
  const list = data.map((val, i) => <li key={`${i}_${val}`}>{val}</li>);
  return isOrdered ? <ol>{list}</ol> : <ul>{list}</ul>;
}
Examples 
const names = ['John', 'Paul', 'Mary'];
ReactDOM.render(<DataList data={names} />, document.getElementById('root'));
ReactDOM.render(<DataList data={names} isOrdered />, document.getElementById('root'));


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DataTable

Renders a table with rows dynamically created from an array of primitives.

  • Render a <table> element with two columns (ID and Value).
  • Use Array.prototype.map to render every item in data as a <tr> element, consisting of its index and value, give it a key produced from the concatenation of the two.
function DataTable({ data }) {
  return (
    <table>
      <thead>
        <tr>
          <th>ID</th>
          <th>Value</th>
        </tr>
      </thead>
      <tbody>
        {data.map((val, i) => (
          <tr key={`${i}_${val}`}>
            <td>{i}</td>
            <td>{val}</td>
          </tr>
        ))}
      </tbody>
    </table>
  );
}
Examples 
const people = ['John', 'Jesse'];
ReactDOM.render(<DataTable data={people} />, document.getElementById('root'));


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MappedTable

Renders a table with rows dynamically created from an array of objects and a list of property names.

  • Use Object.keys(), Array.prototype.filter(), Array.prototype.includes() and Array.prototype.reduce() to produce a filteredData array, containing all objects with the keys specified in propertyNames.
  • Render a <table> element with a set of columns equal to the amount of values in propertyNames.
  • Use Array.prototype.map to render each value in the propertyNames array as a <th> element.
  • Use Array.prototype.map to render each object in the filteredData array as a <tr> element, containing a <td> for each key in the object.
function MappedTable({ data, propertyNames }) {
  let filteredData = data.map(v =>
    Object.keys(v)
      .filter(k => propertyNames.includes(k))
      .reduce((acc, key) => ((acc[key] = v[key]), acc), {})
  );
  return (
    <table>
      <thead>
        <tr>
          {propertyNames.map(val => (
            <th key={`h_${val}`}>{val}</th>
          ))}
        </tr>
      </thead>
      <tbody>
        {filteredData.map((val, i) => (
          <tr key={`i_${i}`}>
            {propertyNames.map(p => (
              <td key={`i_${i}_${p}`}>{val[p]}</td>
            ))}
          </tr>
        ))}
      </tbody>
    </table>
  );
}

Notes

This component does not work with nested objects and will break if there are nested objects inside any of the properties specified in propertyNames.,<!-tags: array,object -->,<!-expertise: 1 -->

Examples 
const people = [
  { name: 'John', surname: 'Smith', age: 42 },
  { name: 'Adam', surname: 'Smith', gender: 'male' }
];
const propertyNames = ['name', 'surname', 'age'];
ReactDOM.render(
  <MappedTable data={people} propertyNames={propertyNames} />,
  document.getElementById('root')
);


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Input

Input

Renders an <input> element that uses a callback function to pass its value to the parent component.

  • Use object destructuring to set defaults for certain attributes of the <input> element.
  • Render an <input> element with the appropriate attributes and use the callback function in the onChange event to pass the value of the input to the parent.
function Input({ callback, type = 'text', disabled = false, readOnly = false, placeholder = '' }) {
  return (
    <input
      type={type}
      disabled={disabled}
      readOnly={readOnly}
      placeholder={placeholder}
      onChange={({ target: { value } }) => callback(value)}
    />
  );
}
Examples 
ReactDOM.render(
  <Input type="text" placeholder="Insert some text here..." callback={val => console.log(val)} />,
  document.getElementById('root')
);


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LimitedTextarea

Renders a textarea component with a character limit.

  • Use the React.useState() hook to create the content state variable and set its value to value. Create a method setFormattedContent, which trims the content of the input if it's longer than limit.
  • Use the React.useEffect() hook to call the setFormattedContent method on the value of the content state variable.
  • Use a<div> to wrap both the<textarea> and the <p> element that displays the character count and bind the onChange event of the <textarea> to call setFormattedContent with the value of event.target.value.
function LimitedTextarea({ rows, cols, value, limit }) {
  const [content, setContent] = React.useState(value);

  const setFormattedContent = text => {
    text.length > limit ? setContent(text.slice(0, limit)) : setContent(text);
  };

  React.useEffect(() => {
    setFormattedContent(content);
  }, []);

  return (
    <div>
      <textarea
        rows={rows}
        cols={cols}
        onChange={event => setFormattedContent(event.target.value)}
        value={content}
      />
      <p>
        {content.length}/{limit}
      </p>
    </div>
  );
}
Examples 
ReactDOM.render(<LimitedTextarea limit={32} value="Hello!" />, document.getElementById('root'));


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LimitedWordTextarea

Renders a textarea component with a word limit.

  • Use the React.useState() hook to create the content and wordCount state variables and set their values to value and 0 respectively.
  • Create a method setFormattedContent, which uses String.prototype.split(' ') to turn the input into an array of words and check if the result of applying Array.prototype.filter(Boolean) has a length longer than limit.
  • If the afforementioned length exceeds the limit, trim the input, otherwise return the raw input, updating content and wordCount accordingly in both cases.
  • Use the React.useEffect() hook to call the setFormattedContent method on the value of the content state variable.
  • Use a<div> to wrap both the<textarea> and the <p> element that displays the character count and bind the onChange event of the <textarea> to call setFormattedContent with the value of event.target.value.
function LimitedWordTextarea({ rows, cols, value, limit }) {
  const [content, setContent] = React.useState(value);
  const [wordCount, setWordCount] = React.useState(0);

  const setFormattedContent = text => {
    let words = text.split(' ');
    if (words.filter(Boolean).length > limit) {
      setContent(
        text
          .split(' ')
          .slice(0, limit)
          .join(' ')
      );
      setWordCount(limit);
    } else {
      setContent(text);
      setWordCount(words.filter(Boolean).length);
    }
  };

  React.useEffect(() => {
    setFormattedContent(content);
  }, []);

  return (
    <div>
      <textarea
        rows={rows}
        cols={cols}
        onChange={event => setFormattedContent(event.target.value)}
        value={content}
      />
      <p>
        {wordCount}/{limit}
      </p>
    </div>
  );
}
Examples 
ReactDOM.render(
  <LimitedWordTextArea limit={5} value="Hello there!" />,
  document.getElementById('root')
);


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MultiselectCheckbox

Renders a checkbox list that uses a callback function to pass its selected value/values to the parent component.

  • Use React.setState() to create a data state variable and set its initial value equal to the options prop.
  • Create a function toggle that is used to toggle the checked to update the data state variable and call the onChange callback passed via the component's props.
  • Render a <ul> element and use Array.prototype.map() to map the data state variable to individual <li> elements with <input> elements as their children.
  • Each <input> element has the type='checkbox' attribute and is marked as readOnly, as its click events are handled by the parent <li> element's onClick handler.
const style = {
  listContainer: {
    listStyle: 'none',
    paddingLeft: 0
  },
  itemStyle: {
    cursor: 'pointer',
    padding: 5
  }
};

function MultiselectCheckbox({ options, onChange }) {
  const [data, setData] = React.useState(options);

  const toggle = item => {
    data.map((_, key) => {
      if (data[key].label === item.label) data[key].checked = !item.checked;
    });
    setData([...data]);
    onChange(data);
  };

  return (
    <ul style={style.listContainer}>
      {data.map(item => {
        return (
          <li key={item.label} style={style.itemStyle} onClick={() => toggle(item)}>
            <input readOnly type="checkbox" checked={item.checked || false} />
            {item.label}
          </li>
        );
      })}
    </ul>
  );
}
Examples 
const options = [{ label: 'Item One' }, { label: 'Item Two' }];

ReactDOM.render(
  <MultiselectCheckbox
    options={options}
    onChange={data => {
      console.log(data);
    }}
  />,
  document.getElementById('root')
);


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PasswordRevealer

Renders a password input field with a reveal button.

  • Use the React.useState() hook to create the shown state variable and set its value to false.
  • Use a<div> to wrap both the<input> and the <button> element that toggles the type of the input field between "text" and "password".
function PasswordRevealer({ value }) {
  const [shown, setShown] = React.useState(false);

  return (
    <div>
      <input type={shown ? 'text' : 'password'} value={value} onChange={() => {}} />
      <button onClick={() => setShown(!shown)}>Show/Hide</button>
    </div>
  );
}
Examples 
ReactDOM.render(<PasswordRevealer />, document.getElementById('root'));


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Select

Renders a <select> element that uses a callback function to pass its value to the parent component.

  • Use object destructuring to set defaults for certain attributes of the <select> element.
  • Render a <select> element with the appropriate attributes and use the callback function in the onChange event to pass the value of the textarea to the parent.
  • Use destructuring on the values array to pass an array of value and text elements and the selected attribute to define the initial value of the <select> element.
function Select({ values, callback, disabled = false, readonly = false, selected }) {
  return (
    <select
      disabled={disabled}
      readOnly={readonly}
      onChange={({ target: { value } }) => callback(value)}
    >
      {values.map(([value, text]) => (
        <option selected={selected === value} value={value}>
          {text}
        </option>
      ))}
    </select>
  );
}
Examples 
let choices = [
  ['grapefruit', 'Grapefruit'],
  ['lime', 'Lime'],
  ['coconut', 'Coconut'],
  ['mango', 'Mango']
];
ReactDOM.render(
  <Select values={choices} selected="lime" callback={val => console.log(val)} />,
  document.getElementById('root')
);


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Slider

Renders a slider element that uses a callback function to pass its value to the parent component.

  • Use object destructuring to set defaults for certain attributes of the <input> element.
  • Render an <input> element of type "range" and the appropriate attributes, use the callback function in the onChange event to pass the value of the input to the parent.
function Slider({ callback, disabled = false, readOnly = false }) {
  return (
    <input
      type="range"
      disabled={disabled}
      readOnly={readOnly}
      onChange={({ target: { value } }) => callback(value)}
    />
  );
}
Examples 
ReactDOM.render(<Slider callback={val => console.log(val)} />, document.getElementById('root'));


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TextArea

Renders a <textarea> element that uses a callback function to pass its value to the parent component.

  • Use object destructuring to set defaults for certain attributes of the <textarea> element.
  • Render a <textarea> element with the appropriate attributes and use the callback function in the onChange event to pass the value of the textarea to the parent.
function TextArea({
  callback,
  cols = 20,
  rows = 2,
  disabled = false,
  readOnly = false,
  placeholder = ''
}) {
  return (
    <textarea
      cols={cols}
      rows={rows}
      disabled={disabled}
      readOnly={readOnly}
      placeholder={placeholder}
      onChange={({ target: { value } }) => callback(value)}
    />
  );
}
Examples 
ReactDOM.render(
  <TextArea placeholder="Insert some text here..." callback={val => console.log(val)} />,
  document.getElementById('root')
);


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Object

TreeView

Renders a tree view of a JSON object or array with collapsible content.

  • Use object destructuring to set defaults for certain props.
  • Use the value of the toggled prop to determine the initial state of the content (collapsed/expanded).
  • Use the React.setState() hook to create the isToggled state variable and give it the value of the toggled prop initially.
  • Return a <div> to wrap the contents of the component and the <span> element, used to alter the component's isToggled state.
  • Determine the appearance of the component, based on isParentToggled, isToggled, name and Array.isArray() on data.
  • For each child in data, determine if it is an object or array and recursively render a sub-tree.
  • Otherwise, render a <p> element with the appropriate style.
.tree-element {
  margin: 0;
  position: relative;
}

div.tree-element:before {
  content: '';
  position: absolute;
  top: 24px;
  left: 1px;
  height: calc(100% - 48px);
  border-left: 1px solid gray;
}

.toggler {
  position: absolute;
  top: 10px;
  left: 0px;
  width: 0;
  height: 0;
  border-top: 4px solid transparent;
  border-bottom: 4px solid transparent;
  border-left: 5px solid gray;
  cursor: pointer;
}

.toggler.closed {
  transform: rotate(90deg);
}

.collapsed {
  display: none;
}

function TreeView({
  data,
  toggled = true,
  name = null,
  isLast = true,
  isChildElement = false,
  isParentToggled = true
}) {
  const [isToggled, setIsToggled] = React.useState(toggled);

  return (
    <div
      style={{ marginLeft: isChildElement ? 16 : 4 + 'px' }}
      className={isParentToggled ? 'tree-element' : 'tree-element collapsed'}
    >
      <span
        className={isToggled ? 'toggler' : 'toggler closed'}
        onClick={() => setIsToggled(!isToggled)}
      />
      {name ? <strong>&nbsp;&nbsp;{name}: </strong> : <span>&nbsp;&nbsp;</span>}
      {Array.isArray(data) ? '[' : '{'}
      {!isToggled && '...'}
      {Object.keys(data).map((v, i, a) =>
        typeof data[v] == 'object' ? (
          <TreeView
            data={data[v]}
            isLast={i === a.length - 1}
            name={Array.isArray(data) ? null : v}
            isChildElement
            isParentToggled={isParentToggled && isToggled}
          />
        ) : (
          <p
            style={{ marginLeft: 16 + 'px' }}
            className={isToggled ? 'tree-element' : 'tree-element collapsed'}
          >
            {Array.isArray(data) ? '' : <strong>{v}: </strong>}
            {data[v]}
            {i === a.length - 1 ? '' : ','}
          </p>
        )
      )}
      {Array.isArray(data) ? ']' : '}'}
      {!isLast ? ',' : ''}
    </div>
  );
}
Examples 
let data = {
  lorem: {
    ipsum: 'dolor sit',
    amet: {
      consectetur: 'adipiscing',
      elit: [
        'duis',
        'vitae',
        {
          semper: 'orci'
        },
        {
          est: 'sed ornare'
        },
        'etiam',
        ['laoreet', 'tincidunt'],
        ['vestibulum', 'ante']
      ]
    },
    ipsum: 'primis'
  }
};
ReactDOM.render(<TreeView data={data} name="data" />, document.getElementById('root'));


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String

Renders a string as plaintext, with URLs converted to appropriate <a> elements.

  • Use String.prototype.split() and String.prototype.match() with a regular expression to find URLs in a string.
  • Return a <React.Fragment> with matched URLs rendered as <a> elements, dealing with missing protocol prefixes if necessary, and the rest of the string rendered as plaintext.
function AutoLink({ text }) {
  const delimiter = /((?:https?:\/\/)?(?:(?:[a-z0-9]?(?:[a-z0-9\-]{1,61}[a-z0-9])?\.[^\.|\s])+[a-z\.]*[a-z]+|(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3})(?::\d{1,5})*[a-z0-9.,_\/~#&=;%+?\-\\(\\)]*)/gi;

  return (
    <React.Fragment>
      {text.split(delimiter).map(word => {
        let match = word.match(delimiter);
        if (match) {
          let url = match[0];
          return <a href={url.startsWith('http') ? url : `http://${url}`}>{url}</a>;
        }
        return word;
      })}
    </React.Fragment>
  );
}
Examples 
ReactDOM.render(
  <AutoLink text="foo bar baz http://example.org bar" />,
  document.getElementById('root')
);


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Visual

Accordion

Renders an accordion menu with multiple collapsible content components.

  • Define an AccordionItem component, pass it to the Accordion and remove unnecessary nodes expect for AccordionItem by identifying the function's name in props.children.
  • Each AccordionItem component renders a <button> that is used to update the Accordion via the props.handleClick callback and the content of the component, passed down via props.children, while its appearance is determined by props.isCollapsed and based on style.
  • In the Accordion component, use the React.useState() hook to initialize the value of the bindIndex state variable to props.defaultIndex.
  • Use Array.prototype.map on the collected nodes to render the individual collapsiple elements.
  • Define changeItem, which will be executed when clicking an AccordionItem's <button>. changeItem executes the passed callback, onItemClick and updates bindIndex based on the clicked element.
function AccordionItem(props) {
  const style = {
    collapsed: {
      display: 'none'
    },
    expanded: {
      display: 'block'
    },
    buttonStyle: {
      display: 'block',
      width: '100%'
    }
  };

  return (
    <div>
      <button style={style.buttonStyle} onClick={() => props.handleClick()}>
        {props.label}
      </button>
      <div
        className="collapse-content"
        style={props.isCollapsed ? style.collapsed : style.expanded}
        aria-expanded={props.isCollapsed}
      >
        {props.children}
      </div>
    </div>
  );
}

function Accordion(props) {
  const [bindIndex, setBindIndex] = React.useState(props.defaultIndex);

  const changeItem = itemIndex => {
    if (typeof props.onItemClick === 'function') props.onItemClick(itemIndex);
    if (itemIndex !== bindIndex) setBindIndex(itemIndex);
  };
  const items = props.children.filter(item => item.type.name === 'AccordionItem');

  return (
    <div className="wrapper">
      {items.map(({ props }) => (
        <AccordionItem
          isCollapsed={bindIndex === props.index}
          label={props.label}
          handleClick={() => changeItem(props.index)}
          children={props.children}
        />
      ))}
    </div>
  );
}
Examples 
ReactDOM.render(
  <Accordion defaultIndex="1" onItemClick={console.log}>
    <AccordionItem label="A" index="1">
      Lorem ipsum
    </AccordionItem>
    <AccordionItem label="B" index="2">
      Dolor sit amet
    </AccordionItem>
  </Accordion>,
  document.getElementById('root')
);


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Renders a carousel component.

  • Use the React.setState() hook to create the active state variable and give it a value of 0 (index of the first item).
  • Use an object, style, to hold the styles for the individual components.
  • Use the React.setEffect() hook to update the value of active to the index of the next item, using setTimeout.
  • Destructure props, compute if visibility style should be set to visible or not for each carousel item while mapping over and applying the combined style to the carousel item component accordingly.
  • Render the carousel items using React.cloneElement() and pass down rest props along with the computed styles.
function Carousel(props) {
  const [active, setActive] = React.useState(0);
  let scrollInterval = null;
  const style = {
    carousel: {
      position: 'relative'
    },
    carouselItem: {
      position: 'absolute',
      visibility: 'hidden'
    },
    visible: {
      visibility: 'visible'
    }
  };
  React.useEffect(() => {
    scrollInterval = setTimeout(() => {
      const { carouselItems } = props;
      setActive((active + 1) % carouselItems.length);
    }, 2000);
  });
  const { carouselItems, ...rest } = props;
  return (
    <div style={style.carousel}>
      {carouselItems.map((item, index) => {
        const activeStyle = active === index ? style.visible : {};
        return React.cloneElement(item, {
          ...rest,
          style: {
            ...style.carouselItem,
            ...activeStyle
          }
        });
      })}
    </div>
  );
}
Examples 
ReactDOM.render(
  <Carousel
    carouselItems={[
      <div>carousel item 1</div>,
      <div>carousel item 2</div>,
      <div>carousel item 3</div>
    ]}
  />,
  document.getElementById('root')
);


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Collapse

Renders a component with collapsible content.

  • Use the React.setState() hook to create the isCollapsed state variable with an initial value of props.collapsed.
  • Use an object, style, to hold the styles for individual components and their states.
  • Use a <div> to wrap both the <button> that alters the component's isCollapsed state and the content of the component, passed down via props.children.
  • Determine the appearance of the content, based on isCollapsed and apply the appropriate CSS rules from the style object.
  • Finally, update the value of the aria-expanded attribute based on isCollapsed to make the component accessible.
function Collapse(props) {
  const [isCollapsed, setIsCollapsed] = React.useState(props.collapsed);

  const style = {
    collapsed: {
      display: 'none'
    },
    expanded: {
      display: 'block'
    },
    buttonStyle: {
      display: 'block',
      width: '100%'
    }
  };

  return (
    <div>
      <button style={style.buttonStyle} onClick={() => setIsCollapsed(!isCollapsed)}>
        {isCollapsed ? 'Show' : 'Hide'} content
      </button>
      <div
        className="collapse-content"
        style={isCollapsed ? style.collapsed : style.expanded}
        aria-expanded={isCollapsed}
      >
        {props.children}
      </div>
    </div>
  );
}
Examples 
ReactDOM.render(
  <Collapse>
    <h1>This is a collapse</h1>
    <p>Hello world!</p>
  </Collapse>,
  document.getElementById('root')
);


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CountDown

Renders a countdown timer that prints a message when it reaches zero.

  • Use object destructuring to set defaults for the hours, minutes and seconds props.
  • Use the React.useState() hook to create the time, paused and over state variables and set their values to the values of the passed props, false and false respectively.
  • Create a method tick, that updates the value of time based on the current value (i.e. decreasing the time by one second).
  • If paused or over is true, tick will return immediately.
  • Create a method reset, that resets all state variables to their initial states.
  • Use the the React.useEffect() hook to call the tick method every second via the use of setInterval() and use clearInterval() to cleanup when the component is unmounted.
  • Use a <div> to wrap a <p> element with the textual representation of the components time state variable, as well as two <button> elements that will pause/unpause and restart the timer respectively.
  • If over is true, the timer will display a message instead of the value of time.
function CountDown({ hours = 0, minutes = 0, seconds = 0 }) {
  const [paused, setPaused] = React.useState(false);
  const [over, setOver] = React.useState(false);
  const [time, setTime] = React.useState({
    hours: parseInt(hours),
    minutes: parseInt(minutes),
    seconds: parseInt(seconds)
  });

  const tick = () => {
    if (paused || over) return;
    if (time.hours == 0 && time.minutes == 0 && time.seconds == 0) setOver(true);
    else if (time.minutes == 0 && time.seconds == 0)
      setTime({
        hours: time.hours - 1,
        minutes: 59,
        seconds: 59
      });
    else if (time.seconds == 0)
      setTime({
        hours: time.hours,
        minutes: time.minutes - 1,
        seconds: 59
      });
    else
      setTime({
        hours: time.hours,
        minutes: time.minutes,
        seconds: time.seconds - 1
      });
  };

  const reset = () => {
    setTime({
      hours: parseInt(hours),
      minutes: parseInt(minutes),
      seconds: parseInt(seconds)
    });
    setPaused(false);
    setOver(false);
  };

  React.useEffect(() => {
    let timerID = setInterval(() => tick(), 1000);
    return () => clearInterval(timerID);
  });

  return (
    <div>
      <p>{`${time.hours.toString().padStart(2, '0')}:${time.minutes
        .toString()
        .padStart(2, '0')}:${time.seconds.toString().padStart(2, '0')}`}</p>
      <div>{over ? "Time's up!" : ''}</div>
      <button onClick={() => setPaused(!paused)}>{paused ? 'Resume' : 'Pause'}</button>
      <button onClick={() => reset()}>Restart</button>
    </div>
  );
}
Examples 
ReactDOM.render(<CountDown hours="1" minutes="45" />, document.getElementById('root'));


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FileDrop

Renders a file drag and drop component for a single file.

  • Create a ref called dropRef for this component.
  • Use the React.useState() hook to create the drag and filename variables, initialized to false and '' respectively. The variables dragCounter and drag are used to determine if a file is being dragged, while filename is used to store the dropped file's name.
  • Create the handleDrag, handleDragIn, handleDragOut and handleDrop methods to handle drag and drop functionality, bind them to the component's context.
  • Each of the methods will handle a specific event, the listeners for which are created and removed in the React.useEffect() hook and its attached cleanup() method.
  • handleDrag prevents the browser from opening the dragged file, handleDragIn and handleDragOut handle the dragged file entering and exiting the component, while handleDrop handles the file being dropped and passes it to props.handleDrop.
  • Return an appropriately styled <div> and use drag and filename to determine its contents and style.
  • Finally, bind the ref of the created <div> to dropRef.
.filedrop {
  min-height: 120px;
  border: 3px solid #d3d3d3;
  text-align: center;
  font-size: 24px;
  padding: 32px;
  border-radius: 4px;
}

.filedrop.drag {
  border: 3px dashed #1e90ff;
}

.filedrop.ready {
  border: 3px solid #32cd32;
}

function FileDrop(props) {
  const [drag, setDrag] = React.useState(false);
  const [filename, setFilename] = React.useState('');
  let dropRef = React.createRef();
  let dragCounter = 0;

  const handleDrag = e => {
    e.preventDefault();
    e.stopPropagation();
  };

  const handleDragIn = e => {
    e.preventDefault();
    e.stopPropagation();
    dragCounter++;
    if (e.dataTransfer.items && e.dataTransfer.items.length > 0) setDrag(true);
  };

  const handleDragOut = e => {
    e.preventDefault();
    e.stopPropagation();
    dragCounter--;
    if (dragCounter === 0) setDrag(false);
  };

  const handleDrop = e => {
    e.preventDefault();
    e.stopPropagation();
    setDrag(false);
    if (e.dataTransfer.files && e.dataTransfer.files.length > 0) {
      props.handleDrop(e.dataTransfer.files[0]);
      setFilename(e.dataTransfer.files[0].name);
      e.dataTransfer.clearData();
      dragCounter = 0;
    }
  };

  React.useEffect(() => {
    let div = dropRef.current;
    div.addEventListener('dragenter', handleDragIn);
    div.addEventListener('dragleave', handleDragOut);
    div.addEventListener('dragover', handleDrag);
    div.addEventListener('drop', handleDrop);
    return function cleanup() {
      div.removeEventListener('dragenter', handleDragIn);
      div.removeEventListener('dragleave', handleDragOut);
      div.removeEventListener('dragover', handleDrag);
      div.removeEventListener('drop', handleDrop);
    };
  });

  return (
    <div
      ref={dropRef}
      className={drag ? 'filedrop drag' : filename ? 'filedrop ready' : 'filedrop'}
    >
      {filename && !drag ? <div>{filename}</div> : <div>Drop files here!</div>}
    </div>
  );
}
Examples 
ReactDOM.render(<FileDrop handleDrop={console.log} />, document.getElementById('root'));


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Mailto

Renders a link formatted to send an email.

  • Destructure the component's props, use email, subject and body to create a <a> element with an appropriate href attribute.
  • Render the link with props.children as its content.
function Mailto({ email, subject, body, ...props }) {
  return (
    <a href={`mailto:${email}?subject=${subject || ''}&body=${body || ''}`}>{props.children}</a>
  );
}
Examples 
ReactDOM.render(
  <Mailto email="foo@bar.baz" subject="Hello" body="Hello world!">
    Mail me!
  </Mailto>,
  document.getElementById('root')
);


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Renders a Modal component, controllable through events. To use the component, import Modal only once and then display it by passing a boolean value to the isVisible attribute.

  • Use object destructuring to set defaults for certain attributes of the modal component.
  • Define keydownHandler, a method which handles all keyboard events, which can be used according to your needs to dispatch actions (e.g. close the modal when Esc is pressed).
  • Use React.useEffect() hook to add or remove the keydown event listener, which calls keydownHandler.
  • Use the isVisible prop to determine if the modal should be shown or not.
  • Use CSS to style and position the modal component.
.modal {
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  right:0;
  width: 100%;
  z-index: 9999;  
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: rgba(0, 0, 0, 0.25);
  animation-name: appear;
  animation-duration: 300ms;
}

.modal-dialog{
  width: 100%;
  max-width: 550px;
  background: white;
  position: relative;
  margin: 0 20px;
  max-height: calc(100vh - 40px);
  text-align: left;
  display: flex;
  flex-direction: column;
  overflow:hidden;
  box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2),0 6px 20px 0 rgba(0,0,0,0.19);
  -webkit-animation-name: animatetop;
  -webkit-animation-duration: 0.4s;
  animation-name: slide-in;
  animation-duration: 0.5s;
}

.modal-header,.modal-footer{
  display: flex;
  align-items: center;
  padding: 1rem;
}
.modal-header{
  border-bottom: 1px solid #dbdbdb;
  justify-content: space-between;
}
.modal-footer{
  border-top: 1px solid #dbdbdb;
  justify-content: flex-end;
}
.modal-close{
  cursor: pointer;
  padding: 1rem;
  margin: -1rem -1rem -1rem auto;
}
.modal-body{
  overflow: auto;
}
.modal-content{
  padding: 1rem;
}

@keyframes appear {
  from {opacity: 0;}
  to {opacity: 1;}
}
@keyframes slide-in {
  from {transform: translateY(-150px);}
  to { transform: translateY(0);}
}

function Modal({ isVisible = false, title, content, footer, onClose }){  
  React.useEffect(() => {
    document.addEventListener('keydown', keydownHandler);
    return () => document.removeEventListener('keydown', keydownHandler);
  });

  function keydownHandler({ key }) {
    switch (key) {
      case 'Escape':  onClose(); break;
      default:
    }
  }

  return !isVisible ? null : (
    <div className="modal" onClick={onClose}>
        <div className="modal-dialog"  onClick={e => e.stopPropagation()}>
        <div className="modal-header">
          <h3 className="modal-title">{title}</h3>
          <span className="modal-close" onClick={onClose}>&times;</span>
        </div>
        <div className="modal-body">
          <div className="modal-content">{ content }</div>
        </div>
        {footer && <div className="modal-footer">{footer}</div>}
      </div>
    </div>
  )
}
Examples 
//Add the component to the render function
function App() {
  const [ isModal, setModal] = React.useState(false);
  
  return (
    <React.Fragment>
      <button onClick={()=> setModal(true)}>Click Here</button>
      <Modal 
        isVisible={ isModal }
        title= "Modal Title"
        content = {<p>Add your content here</p>}
        footer = {<button>Cancel</button>}
        onClose ={()=> setModal(false)}
      />
    </React.Fragment>
  )
}

ReactDOM.render( <App/>, document.getElementById('root'));


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StarRating

Renders a star rating component.

  • Define a component, called Star that will render each individual star with the appropriate appearance, based on the parent component's state.
  • In the StarRating component, use the React.useState() hook to define the rating and selection state variables with the initial values of props.rating (or 0 if invalid or not supplied) and 0.
  • Create a method, hoverOver, that updates selected and rating according to the provided event.
  • Create a <div> to wrap the <Star> components, which are created using Array.prototype.map on an array of 5 elements, created using Array.from, and handle the onMouseLeave event to set selection to 0, the onClick event to set the rating and the onMouseOver event to set selection to the star-id attribute of the event.target respectively.
  • Finally, pass the appropriate values to each <Star> component (starId and marked).
function Star({ marked, starId }) {
  return (
    <span star-id={starId} style={{ color: '#ff9933' }} role="button">
      {marked ? '\u2605' : '\u2606'}
    </span>
  );
}

function StarRating(props) {
  const [rating, setRating] = React.useState(typeof props.rating == 'number' ? props.rating : 0);
  const [selection, setSelection] = React.useState(0);
  const hoverOver = event => {
    let val = 0;
    if (event && event.target && event.target.getAttribute('star-id'))
      val = event.target.getAttribute('star-id');
    setSelection(val);
  };
  return (
    <div
      onMouseOut={() => hoverOver(null)}
      onClick={(event) => setRating(event.target.getAttribute('star-id') || rating)}
      onMouseOver={hoverOver}
    >
      {Array.from({ length: 5 }, (v, i) => (
        <Star
          starId={i + 1}
          key={`star_${i + 1} `}
          marked={selection ? selection >= i + 1 : rating >= i + 1}
        />
      ))}
    </div>
  );
}
Examples 
ReactDOM.render(<StarRating />, document.getElementById('root'));
ReactDOM.render(<StarRating rating={2} />, document.getElementById('root'));


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Tabs

Renders a tabbed menu and view component.

  • Define a TabItem component, pass it to the Tab and remove unnecessary nodes expect for TabItem by identifying the function's name in props.children.
  • Use the React.useState() hook to initialize the value of the bindIndex state variable to props.defaultIndex.
  • Use Array.prototype.map on the collected nodes to render the tab-menu and tab-view.
  • Define changeTab, which will be executed when clicking a <button> from the tab-menu.
  • changeTab executes the passed callback, onTabClick and updates bindIndex, which in turn causes a re-render, evaluating the style and className of the tab-view items and tab-menu buttons according to their index.
.tab-menu > button {
  cursor: pointer;
  padding: 8px 16px;
  border: 0;
  border-bottom: 2px solid transparent;
  background: none;
}
.tab-menu > button.focus {
  border-bottom: 2px solid #007bef;
}
.tab-menu > button:hover {
  border-bottom: 2px solid #007bef;
}

function TabItem(props) {
  return <div {...props} />;
}

function Tabs(props) {
  const [bindIndex, setBindIndex] = React.useState(props.defaultIndex);
  const changeTab = newIndex => {
    if (typeof props.onTabClick === 'function') props.onTabClick(newIndex);
    setBindIndex(newIndex);
  };
  const items = props.children.filter(item => item.type.name === 'TabItem');

  return (
    <div className="wrapper">
      <div className="tab-menu">
        {items.map(({ props: { index, label } }) => (
          <button onClick={() => changeTab(index)} className={bindIndex === index ? 'focus' : ''}>
            {label}
          </button>
        ))}
      </div>
      <div className="tab-view">
        {items.map(({ props }) => (
          <div
            {...props}
            className="tab-view_item"
            key={props.index}
            style={{ display: bindIndex === props.index ? 'block' : 'none' }}
          />
        ))}
      </div>
    </div>
  );
}
Examples 
ReactDOM.render(
  <Tabs defaultIndex="1" onTabClick={console.log}>
    <TabItem label="A" index="1">
      Lorem ipsum
    </TabItem>
    <TabItem label="B" index="2">
      Dolor sit amet
    </TabItem>
  </Tabs>,
  document.getElementById('root')
);


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Ticker

Renders a ticker component.

  • Use the React.useState() hook to initialize the ticker state variable to 0.
  • Define two methods, tick and reset, that will periodically increment timer based on interval and reset interval respectively.
  • Return a <div> with two <button> elements, each of which calls tick and reset respectively.
function Ticker(props) {
  const [ticker, setTicker] = React.useState(0);
  let interval = null;

  const tick = () => {
    reset();
    interval = setInterval(() => {
      if (ticker < props.times) setTicker(ticker + 1);
      else clearInterval(interval);
    }, props.interval);
  };

  const reset = () => {
    setTicker(0);
    clearInterval(interval);
  };

  return (
    <div>
      <span style={{ fontSize: 100 }}>{this.state.ticker}</span>
      <button onClick={this.tick}>Tick!</button>
      <button onClick={this.reset}>Reset</button>
    </div>
  );
}
Examples 
ReactDOM.render(<Ticker times={5} interval={1000} />, document.getElementById('root'));


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Toggle

Renders a toggle component.

  • Use the React.useState() to initialize the isToggleOn state variable to false.
  • Use an object, style, to hold the styles for individual components and their states.
  • Return a <button> that alters the component's isToggledOn when its onClick event is fired and determine the appearance of the content based on isToggleOn, applying the appropriate CSS rules from the style object.
function Toggle(props) {
  const [isToggleOn, setIsToggleOn] = React.useState(false);
  style = {
    on: {
      backgroundColor: 'green'
    },
    off: {
      backgroundColor: 'grey'
    }
  };

  return (
    <button onClick={() => setIsToggleOn(!isToggleOn)} style={isToggleOn ? style.on : style.off}>
      {isToggleOn ? 'ON' : 'OFF'}
    </button>
  );
}
Examples 
ReactDOM.render(<Toggle />, document.getElementById('root'));


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Tooltip

Renders a tooltip component.

  • Use the React.useState() hook to create the show variable and initialize it to false.
  • Return a <div> element that contains the <div> that will be the tooltip and the children passed to the component.
  • Handle the onMouseEnter and onMouseLeave methods, by altering the value of the show variable.
.tooltip {
  position: relative;
  background: rgba(0, 0, 0, 0.7);
  color: white;
  visibility: hidden;
  padding: 5px;
  border-radius: 5px;
}
.tooltip-arrow {
  position: absolute;
  top: 100%;
  left: 50%;
  border-width: 5px;
  border-style: solid;
  border-color: rgba(0, 0, 0, 0.7) transparent transparent;
}

function Tooltip({ children, text, ...rest }) {
  const [show, setShow] = React.useState(false);

  return (
    <div>
      <div className="tooltip" style={show ? { visibility: 'visible' } : {}}>
        {text}
        <span className="tooltip-arrow" />
      </div>
      <div {...rest} onMouseEnter={() => setShow(true)} onMouseLeave={() => setShow(false)}>
        {children}
      </div>
    </div>
  );
}
Examples 
ReactDOM.render(
  <Tooltip text="Simple tooltip">
    <button>Hover me!</button>
  </Tooltip>,
  document.getElementById('root')
);


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This repository is a work in progress. If you want to contribute, please check the open issues to see where and how you can help out!

This README is built using markdown-builder.

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