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Events Live Cheatsheet

Live examples of common React events, including usage of common properties on their event objects.

This cheatsheet contains live examples of a number of common React events. You can learn more about events in the Everything About Events chapter of Learn React By Itself.

There are still a number of events with no examples, but I will be adding more! For a full reference without examples, you can see React’s official documentation. If there are any events in particular that you’d like to see examples for, drop me a line at james@sevenstripes.com.

Keyboard

Keyboard events can be used with any focusable element. This includes HTML form elements, as well as any element with a tabIndex property.

onKeyDown is called when a key is depressed
onKeyPress is called after the key is released, but before onKeyUp is triggered
onKeyUp is called last, after the key is pressed

Event object summary

To check the key that was pressed, use the key property. This holds a string that represents the key.

The altKey, ctrlKey, metaKey and shiftKey properties let you check if a modifier key was depressed at the time of the event. These are all booleans.

A numeric keyCode property is also available, but try to avoid this as it will make your code harder to read.

Examples

Order of events and available properties

function handler(event) {
  alert(`
    key: ${event.key}
    keyCode: ${event.keyCode}
    altKey: ${event.altKey}
    ctrlKey: ${event.ctrlKey}
    metaKey: ${event.metaKey}
    shiftKey: ${event.shiftKey}
  `)
}

ReactDOM.render(
  <input
    placeholder='Hit a key...'
    onKeyDown={handler}
    onKeyPress={handler}
    onKeyUp={handler}
  />,
  document.getElementById('app')
)

Keyboard events on non-form elements

ReactDOM.render(
  <div>
    <p tabIndex={-1}
       style={{ backgroundColor: 'lightgreen' }}
       onKeyDown={event => alert(event.key)}>
      Click to focus, then hit a key.
    </p>
    
    <p style={{ backgroundColor: 'pink' }}
       onKeyDown={event => alert(event.keyCode)}>
      No tabIndex means no keyboard events
    </p>
  </div>,
  document.getElementById('app')
)

Focus

onBlur is called when a control loses focus
onFocus is called when a control receives focus

When switching between elements, onBlur will always be called before onFocus.

Event object summary

It is probably best to avoid the event object for focus events, as browser support for the underlying events varies significantly. In particular, the preventDefault() method will not work reliably.

Example

See how focus and blur events are fired by clicking on a button, and using the Tab or shift-Tab key combinations to navigate between them.

function render(history=[]) {
  function handleFocus(n) { render(history.concat(<div>focused {n}</div>)) }
  function handleBlur(n) { render(history.concat(<div>blurred {n}</div>)) }

  ReactDOM.render(
    <div>
      <button onFocus={handleFocus.bind(null, 1)}
              onBlur={handleBlur.bind(null, 1)}>
        Button 1
      </button>
      <br />
      <button onFocus={handleFocus.bind(null, 2)}
              onBlur={handleBlur.bind(null, 2)}>
         Button 2
      </button>
      <div style={{height: 400, overflow: 'scroll'}}>{history}</div>
    </div>,
    document.getElementById('app')
  )
}
render()

Form

onChange is called when the user changes the value in a form control.
onInput is identical to onChange. Prefer onChange where possible.
onSubmit is a special prop for <form> elements that is called when a <button type='submit'> is pressed, or when the user hits the return key within a field.

Event object summary

For onChange, the event.target object allows you to acces the control’s DOM node. You can then use event.target.value to get the new value that was entered into the control.

The event.preventDefault() method allows you to prevent default behavior. When used within onSubmit, this will prevent the browser from navigating to a new page. When used within onChange, it will prevent whatever character was entered from being added to the control.

Examples

Modifying user input

function render(value='') {
  ReactDOM.render(
    <input value={'$'+value}
           onChange={event => render(event.target.value.replace(/^\$/, ''))}
    />,
    document.getElementById('app')
  )
}
render()

Preventing navigation on form submission

// Without `event.preventDefault()`, pressing submit will cause the browser
// to reload the page.
ReactDOM.render(
  <form onSubmit={event => { event.preventDefault(); alert('submitted') }}>
    <input placeholder='Press enter to submit' /><br />
    <button type='submit'>Submit</button>
  </form>,
  document.getElementById('app')
)

Mouse

onClick: a mouse button was pressed and released. Called before onMouseUp.
onContextMenu: the right mouse button was pressed.
onDoubleClick
onMouseDown: a mouse button is depressed
onMouseEnter: the mouse moves over an element or its children
onMouseLeave: the mouse leaves an element
onMouseMove
onMouseOut: the mouse moves off of an element, or onto one of its children
onMouseOver: the mouse moves directly over an element
onMouseUp: a mouse button was released

React’s drag and drop events have access to the same event object properties as the mouse events. However, I’d recommend using react-dnd instead of using the raw events where possible. For reference, the drag/drop events are:

onDrag onDragEnd onDragEnter onDragExit onDragLeave onDragOver onDragStart onDrop

Event object summary

The button property holds a number that represents which mouse button was pressed. This will be 0 for the left button and 1 for the middle button. Theoretically, 2 represents the right button, but most browsers will not trigger any events other than onContextMenu when the right button is pressed.

The properties altKey, ctrlKey, metaKey and shiftKey allow you to check if a modifier key was pressed on your keyboard when the event was triggered, just like with keyboard events. These are all booleans.

The preventDefault() method can be used to cancel default click actions. For example, to prevent the browser from navigating when a link is clicked, you can call event.preventDefault() within an <a> element’s onClick handler.

There are also a number of positioning properties:

clientX and clientY contain the coordinates measured from the top left of the visible part of the page (regardless of the scroll position)
pageX and pageY contain the coordinates from the top of the page – which may be currently off-screen due to scrolling.
screenX and screenY give the position within the entire screen.

Examples

Visualizing mouse position

Hover your mouse over the preview area to see the values of the positioning properties.

const style =
  {position:'absolute',top:0,left:0,right:0,bottom:0,backgroundColor:'beige'}
function render(event, show) {
  ReactDOM.render(
    <div onMouseMove={(event) => render(Object.assign({}, event), show)}
         onMouseEnter={(event) => render(Object.assign({}, event), true)}
         onMouseLeave={(event) => render(Object.assign({}, event), false)}
         style={style}>
       {show &&
       <div style={{position:'fixed',top:event.clientY,left:event.clientX}}>
         clientX: {event.clientX}<br />
         clientY: {event.clientY}<br />
         pageX: {event.pageX}<br />
         pageY: {event.pageY}<br />
         screenX: {event.screenX}<br />
         screenY: {event.screenY}<br />
       </div>}
    </div>,
    document.getElementById('app')
  )
}
render({}, false)

Without event.preventDefault(), clicking the link in the preview pane would reload the page.

ReactDOM.render(
  <a onClick={e => e.preventDefault()}
     href='/resources/react-events-cheatsheet'>
    React Events Cheatsheet
  </a>,
  document.getElementById('app')
)

Right mouse button events

Try left and right clicking the different buttons to see whether the events work.

function showButton(event) {
  event.preventDefault()
  alert(event.button == 2 ? 'right' : 'not right')
}

ReactDOM.render(
  <div>
    <button onClick={showButton}
            onMouseUp={showButton}>
      Right button events don't work reliably with onClick or OnMouseUp
    </button><br/>
    <button onMouseDown={showButton}>
      preventDefault stops right button events from working with onMouseDown
    </button><br/>
    <button onContextMenu={showButton}>
      Only right button events work with onContextMenu
    </button>
  </div>,
  document.getElementById('app')
)

onMouseEnter/onMouseLeave vs. onMouseOver/onMouseOut

Note how onMouseEnter and onMouseLeave are only called when you move your mosue over the red box, while onMouseOver and onMouseOut are called when the mouse movers over the blue child too.

let enter = 0, leave = 0, over = 0, out = 0
function render() {
  ReactDOM.render(
    <div style={{width: 200, height: 200, backgroundColor: 'red'}}
         onMouseEnter={() => { enter++; render() }}
         onMouseLeave={() => { leave++; render() }}
         onMouseOver={() => { over++; render() }}
         onMouseOut={() => { out++; render() }}>
      Enter called {enter} times<br />
      Leave called {leave} times<br />
      Over called {over} times<br />
      Out called {out} times<br />
      <div style={{width: 100, height: 100, backgroundColor: 'blue'}}>
      
      </div>
    </div>,
    document.getElementById('app')
  )
}
render()

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