canplay

16 March, 2023

Contributors

Milsaware

@milsaware

About

The canplay event is triggered when a media element, such as an HTML5 <video> or <audio> element, has enough data available to start playing without interruption. This event is useful for checking whether a media element is ready to play before attempting to start playback.

When a media element is loaded, it may take some time for enough data to be downloaded to the client device to allow for smooth playback. The canplay event is triggered when the browser has determined that enough data has been buffered to allow for uninterrupted playback.

The canplay event can be used to perform actions once a media element is ready to play, such as updating the UI to show that the media is loaded and ready, or automatically starting playback.

Event listener

Here is an example of how to use the canplay event with an event handler

HTML

<audio controls>
    <source src="media.mp3" type="audio/mpeg">
</audio>

JavaScript

const audio = document.querySelector('audio');

audio.addEventListener('canplay', function () {
    console.log('Media file can be played!');
    // Perform some action here, such as displaying a play button or adding some text.
});

Here, the canplay event is added to the audio element using the addEventListener() method. The callback function will be executed when the media file can be played. Inside the callback function, we can perform some action, such as displaying a play button or adding some text.

Note that the controls attribute is added to the audio element to display the default controls for the media player. You can customize the appearance of the media player using CSS.

Also, note that the canplay event may not be supported by all browsers. You may need to use alternative events, such as canplaythrough or loadedmetadata, depending on your requirements.

Property

There is an oncanplay property that can be used to attach an event handler function to the canplay event for a media element:

const videoElement = document.querySelector('#myVideo');

videoElement.oncanplay = function(event) {
    // Perform some action when the video is ready to play
    console.log('Video is ready to play');
};

Here, the oncanplay property is used to assign an anonymous function as the event handler for the canplay event of the videoElement.

It's worth noting that using the addEventListener method is generally considered a better practice than using the on properties, as it allows for attaching multiple event listeners to the same event, removing event listeners, and gives more control over event propagation. However, the oncanplay property can be a useful shorthand for quickly attaching a single event listener for simple use cases.

Inline

The canplay event can also be used inline in HTML using the oncanplay attribute as follows:

<audio controls oncanplay="handleCanPlay()">
    <source src="media.mp3" type="audio/mpeg">
</audio>

Here, the oncanplay attribute is added to the audio element. This attribute contains the JavaScript code that will be executed when the canplay event is triggered. In this case, the code calls the handleCanPlay() function.

Note that using inline event handlers can make your code harder to read and maintain, especially if you have a lot of them. It's generally considered better practice to separate your JavaScript code from your HTML code by using event listeners.

Programmatic trigger

There is no canplay() method to trigger the canplay event programmatically. The canplay event is triggered automatically by the browser when it determines that the media file can be played, based on its current buffering state.

However, it is possible to programmatically trigger the canplay event using the dispatchEvent method. The dispatchEvent method can be used to simulate the event on an element, which can be useful in cases where you need to manually trigger an event handler function or simulate a user interaction:

const videoElement = document.querySelector('#myVideo');

// Simulate the canplay event
const canPlayEvent = new Event('canplay');
videoElement.dispatchEvent(canPlayEvent);

Here, the dispatchEvent method is used to create a new canplay event using the Event constructor, and then the event is triggered on the videoElement using the dispatchEvent method.

Note that triggering events programmatically can be useful in certain cases, but it should be used with caution as it can result in unexpected behaviour if not used properly. It's generally recommended to let events be triggered naturally by user interaction or system events, and to only use dispatchEvent when necessary.

javascript