16 KiB
jsPsych.pluginAPI
The pluginAPI module contains functions that are useful when developing new plugins.
jsPsych.pluginAPI.autoPreload
jsPsych.pluginAPI.autoPreload(timeline, callback)
Parameters
| Parameter | Type | Description |
|---|---|---|
| timeline | TimelineNode object | A TimelineNode object that contains an arbitrary set of trials. |
| callback | function | A function to execute when loading is complete |
Return value
Returns nothing.
Description
Attempts to preload all image files and audio files that will be used to run the trials on the timeline. Content will only preload from plugins that have used the registerPreload method to define the media types of their parameters.
The callback function executes once all of the files are preloaded.
This method is used internally by the core jsPsych code. It is not recommended that you call it manually.
Examples
// you probably shouldn't use this method
jsPsych.pluginAPI.cancelAllKeyboardResponses
jsPsych.pluginAPI.cancelAllKeyboardResponses()
Parameters
None.
Return value
Returns nothing.
Description
Cancels all currently active keyboard listeners created by jsPsych.pluginAPI.getKeyboardResponse.
Examples
jsPsych.pluginAPI.cancelAllKeyboardResponses();
jsPsych.pluginAPI.cancelKeyboardResponse
jsPsych.pluginAPI.cancelKeyboardResponse(listener_id)
Parameters
| Parameter | Type | Description |
|---|---|---|
| listener_id | object | The listener_id object generated by the call to jsPsych.pluginAPI.getKeyboardResponse. |
Return value
Returns nothing.
Description
Cancels a specific keyboard listener created by jsPsych.pluginAPI.getKeyboardResponse.
Examples
// create a persistent keyboard listener
var listener_id = jsPsych.pluginAPI.getKeyboardResponse({
callback_function: after_response,
valid_responses: ['p','q'],
rt_method: 'performance',
persist: true,
allow_held_key: false
});
// cancel keyboard listener
jsPsych.pluginAPI.cancelKeyboardResponse(listener_id);
jsPsych.pluginAPI.clearAllTimeouts
jsPsych.pluginAPI.clearAllTimeouts()
Parameters
None.
Return value
Returns nothing.
Description
Clears any pending timeouts that were set using jsPsych.pluginAPI.setTimeout()
jsPsych.pluginAPI.compareKeys
jsPsych.pluginAPI.compareKeys(key1, key2)
Parameters
| Parameter | Type | Description |
|---|---|---|
| key1 | string or numeric | The representation of a key, either string or keycode |
| key2 | string or numeric | The representation of a key, either string or keycode |
Return value
Returns true if keycodes or strings refer to the same key, regardless of type.
Description
Compares two keys to see if they are the same, ignoring differences in representational type.
Examples
jsPsych.pluginAPI.compareKeys('a', 65);
// returns true
jsPsych.pluginAPI.convertKeyCharacterToKeyCode('space', 31)
// returns false
jsPsych.pluginAPI.convertKeyCharacterToKeyCode
jsPsych.pluginAPI.convertKeyCharacterToKeyCode(character)
Parameters
| Parameter | Type | Description |
|---|---|---|
| character | string | The string representation of keyboard key. |
Return value
Returns the numeric keycode associated with the character parameter.
Description
Converts between the string representation of a key and the numeric key code associated with that key.
Examples
var keycode = jsPsych.pluginAPI.convertKeyCharacterToKeyCode('a')
// keycode is 65
keycode = jsPsych.pluginAPI.convertKeyCharacterToKeyCode('space')
// keycode is 32
jsPsych.pluginAPI.convertKeyCodeToKeyCharacter
jsPsych.pluginAPI.convertKeyCodeToKeyCharacter(character)
Parameters
| Parameter | Type | Description |
|---|---|---|
| code | numeric | The numeric representation of keyboard key. |
Return value
Returns the string representation of the key associated with the code parameter.
Description
Converts between the numeric key code of a key and the string representation associated with that key.
Examples
var keycode = jsPsych.pluginAPI.convertKeyCharacterToKeyCode(65)
// key is 'a'
keycode = jsPsych.pluginAPI.convertKeyCharacterToKeyCode(32)
// keycode is 'space'
jsPsych.pluginAPI.getAudioBuffer
jsPsych.pluginAPI.getAudioBuffer(filepath)
Parameters
| Parameter | Type | Description |
|---|---|---|
| filepath | string | The path to the audio file that was preloaded. |
Return value
Returns buffered audio file for playback. If the browser supports it the buffer will be playable with the WebAudio API. Otherwise, the returned buffer will be an HTML5 Audio object.
Description
Gets an AudioBuffer that can be played with the WebAudio API or an Audio object that can be played with HTML5 Audio. The file must be preloaded with preloadAudioFiles or the automatic preload (autoPreload).
Examples
// the code below is used to play audio in the audio-keyboard-response plugin
var source = context.createBufferSource();
source.buffer = jsPsych.pluginAPI.getAudioBuffer(trial.stimulus);
source.connect(context.destination);
startTime = context.currentTime;
source.start(startTime);
jsPsych.pluginAPI.getKeyboardResponse
jsPsych.pluginAPI.getKeyboardResponse(parameters)
Parameters
The method accepts an object of parameter values (see example below). The valid keys for this object are listed in the table below.
| Parameter | Type | Description |
|---|---|---|
| callback_function | function | The function to execute whenever a valid keyboard response is generated. |
| valid_responses | array | An array of key codes or character strings representing valid responses. Responses not on the list will be ignored. An empty array indicates that all responses are acceptable. |
| rt_method | string | Indicates which method of recording time to use. The 'performance' method uses calls to performance.now(), which is the standard way of measuring timing in jsPsych. It is supported by up-to-date versions of all the major browsers. The audio method is used in conjuction with an audio_context (set as an additional parameter). This uses the clock time of the audio_context when audio stimuli are being played. |
| audio_context | AudioContext object | The AudioContext of the audio file that is being played. |
| audio_context_start_time | numeric | The scheduled time of the sound file in the AudioContext. This will be used as the start time. |
| allow_held_key | boolean | If true, then responses will be registered from keys that are being held down. If false, then a held key can only register a response the first time that getKeyboardResponse is called for that key. For example, if a participant holds down the A key before the experiment starts, then the first time getKeyboardResponse is called, the A will register as a key press. However, any future calls to getKeyboardResponse will not register the A until the participant releases the key and presses it again. |
| persist | boolean | If false, then the keyboard listener will only trigger the first time a valid key is pressed. If true, then it will trigger every time a valid key is pressed until it is explicitly cancelled by jsPsych.pluginAPI.cancelKeyboardResponse or jsPsych.pluginAPI.cancelAllKeyboardResponses. |
Return value
Return an object that uniquely identifies the keyboard listener. This object can be passed to jsPsych.pluginAPI.cancelKeyboardResponse to cancel the keyboard listener.
Description
Gets a keyboard response from the subject, recording the response time from when the function is first called until a valid response is generated.
The keyboard event listener will be bound to the display_element declared in jsPsych.init() (or the <body> element if no display_element is specified). This allows jsPsych experiments to be embedded in websites with other content without disrupting the functionality of other UI elements.
A valid response triggers the callback_function specified in the parameters. A single argument is passed to the callback function. The argument contains an object with the properties key and rt. key contains the numeric key code of the response, and rt contains the response time.
Examples
Get a single response from any key
var after_response = function(info){
alert('You pressed key '+info.key+' after '+info.rt+'ms');
}
jsPsych.pluginAPI.getKeyboardResponse({
callback_function:after_response,
valid_responses: jsPsych.ALL_KEYS,
rt_method: 'performance',
persist: false
});
Get a responses from a key until the letter Q is pressed
var after_response = function(info){
alert('You pressed key '+info.key+' after '+info.rt+'ms');
if(info.key == 81){ // the key code for 'Q' is 81.
jsPsych.pluginAPI.cancelKeyboardResponse(listener);
}
}
var listener = jsPsych.pluginAPI.getKeyboardResponse({
callback_function:after_response,
valid_responses: jsPsych.ALL_KEYS,
rt_method: 'performance',
persist: true
});
jsPsych.pluginAPI.preloadAudioFiles
jsPsych.pluginAPI.preloadAudioFiles(files, callback_complete, callback_load)
Parameters
| Parameter | Type | Description |
|---|---|---|
| files | array | An array of audio file paths to load. The array can be nested (e.g., if images are in multiple arrays to help sort by condition or task). |
| callback_complete | function | A function to execute when all the files have been loaded. |
| callback_load | function | A function to execute after each file has been loaded. A single parameter is passed to this function which contains the number of files that have been loaded so far. |
Return value
Returns nothing.
Description
Use this function to preload audio files that are not part of a plugin with automatic preloading. Audio files in official plugins will automatically preload. See Media Preloading for more information.
It is possible to run this function without specifying a callback function. However, in this case the code will continue executing while the files are loaded. Thus, it is possible that an audio file would be required for playing before it is done preloading. The callback_complete function will only execute after all the audio files are loaded, and can be used to control the flow of the experiment (e.g., by starting the experiment in the callback_complete function).
The callback_load function can be used to indicate progress. See example below.
Examples
Basic use
var sounds = ['file1.mp3', 'file2.mp3', 'file3.mp3'];
jsPsych.pluginAPI.preloadAudioFiles(sounds, function(){ startExperiment(); });
function startExperiment(){
jsPsych.init({
timeline: exp
});
}
Show progress of loading
var sounds = ['file1.mp3', 'file2.mp3', 'file3.mp3'];
jsPsych.pluginAPI.preloadAudioFiles(sounds, function(){ startExperiment(); }, function(nLoaded) { updateLoadedCount(nLoaded); });
function updateLoadedCount(nLoaded){
var percentcomplete = nLoaded / sounds.length * 100;
// could put something fancier here, like a progress bar
// or updating text in the DOM.
console.log('Loaded '+percentcomplete+'% of audio files');
}
function startExperiment(){
jsPsych.init({
timeline: exp
});
}
jsPsych.pluginAPI.preloadImages
jsPsych.pluginAPI.preloadImages(images, callback_complete, callback_load)
Parameters
| Parameter | Type | Description |
|---|---|---|
| images | array | An array of image paths to load. The array can be nested (e.g., if images are in multiple arrays to help sort by condition or task). |
| callback_complete | function | A function to execute when all the images have been loaded. |
| callback_load | function | A function to execute after each image has been loaded. A single parameter is passed to this function which contains the number of images that have been loaded so far. |
Return value
Returns nothing.
Description
Use this function to preload image files that are not part of a plugin with automatic preloading. Image files in official plugins will automatically preload. See Media Preloading for more information.
It is possible to run this function without specifying a callback function. However, in this case the code will continue executing while the images are loaded. Thus, it is possible that an image would be required for display before it is done preloading. The callback_complete function will only execute after all the images are loaded, and can be used to control the flow of the experiment (e.g., by starting the experiment in the callback_complete function).
The callback_load function can be used to indicate progress, if the number of images to be loaded is known ahead of time. See example below.
Examples
Basic use
var images = ['img/file1.png', 'img/file2.png', 'img/file3.png'];
jsPsych.pluginAPI.preloadImages(images, function(){ startExperiment(); });
function startExperiment(){
jsPsych.init({
timeline: exp
});
}
Show progress of loading
var images = ['img/file1.png', 'img/file2.png', 'img/file3.png'];
jsPsych.pluginAPI.preloadImages(images, function(){ startExperiment(); }, function(nLoaded) { updateLoadedCount(nLoaded); });
function updateLoadedCount(nLoaded){
var percentcomplete = nLoaded / images.length * 100;
// could put something fancier here, like a progress bar
// or updating text in the DOM.
console.log('Loaded '+percentcomplete+'% of images');
}
function startExperiment(){
jsPsych.init({
timeline: exp
});
}
jsPsych.pluginAPI.registerPreload
jsPsych.pluginAPI.registerPreload(plugin_name, parameter, media_type, conditional_function)
Parameters
| Parameter | Type | Description |
|---|---|---|
| plugin_name | string | The name of the plugin. e.g., 'image-keyboard-response'. |
| parameter | string | The name of the parameter that is a media file. e.g., 'stimulus' |
| media_type | string | The type of media, either 'image', 'audio' or 'video'. |
| conditional_function | function | Only run the preload for a trial if this function returns true, or if this function does not exist. |
Return value
Nothing.
Description
Use this method in a plugin file to mark a parameter as containing an element that should be preloaded. The method should be called in the plugin file such that it gets called when the file is loaded.
The conditional_function function is passed a single argument containing the trial object.
Example
For an example, see the image-keyboard-response and audio-keyboard-response plugins.
jsPsych.pluginAPI.setTimeout
jsPsych.pluginAPI.setTimeout(callback, delay)
Parameters
| Parameter | Type | Description |
|---|---|---|
| callback | function | A function to execute after waiting for delay. |
| delay | integer | Time to wait in milliseconds. |
Return value
Returns the ID of the setTimeout handle.
Description
This is simply a call to the standard setTimeout function in JavaScript with the added benefit of registering the setTimeout call in a central list. This is useful for scenarios where some other event (the trial ending, aborting the experiment) should stop the execution of queued timeouts.
Examples
// print the time
console.log(Date.now())
// print the time 1s later
jsPsych.pluginAPI.setTimeout(function(){
console.log(Date.now())
}, 1000);