jsPsych¶

initJsPsych¶

var jsPsych = initJsPsych(settings);

Parameters¶

Parameter	Type	Description
settings	object	The settings object for initializing jsPsych. See table below.

The settings object can contain several parameters. None of the parameters are required.

Parameter	Type	Description
display_element	string	The ID of an HTML element to display the experiment in. If left blank, jsPsych will use the `<body>` element to display content. All keyboard event listeners are bound to this element. In order for a keyboard event to be detected, this element must have focus (be the last thing that the participant clicked on).
on_finish	function	Function to execute when the experiment ends.
on_trial_start	function	Function to execute when a new trial begins.
on_trial_finish	function	Function to execute when a trial ends.
on_data_update	function	Function to execute every time data is stored using the `jsPsych.data.write` method. All plugins use this method to save data (via a call to `jsPsych.finishTrial`, so this function runs every time a plugin stores new data.
on_interaction_data_update	function	Function to execute every time a new interaction event occurs. Interaction events include clicking on a different window (blur), returning to the experiment window (focus), entering full screen mode (fullscreenenter), and exiting full screen mode (fullscreenexit).
on_close	function	Function to execute when the user leaves the page. Can be used, for example, to save data before the page is closed.
show_progress_bar	boolean	If `true`, then a progress bar is shown at the top of the page. Default is `false`.
message_progress_bar	string or function	Message to display next to the progress bar or a function that returns that message. The default is 'Completion Progress'. If `message_progress_bar` is a function, it receives one single argument which is the current progress, ranging from 0 to 1; the function gets called on every progress bar update automatically.
auto_update_progress_bar	boolean	If true, then the progress bar at the top of the page will automatically update as every top-level timeline or trial is completed.
use_webaudio	boolean	If false, then jsPsych will not attempt to use the WebAudio API for audio playback. Instead, HTML5 Audio objects will be used. The WebAudio API offers more precise control over the timing of audio events, and should be used when possible. The default value is `true`.
default_iti	numeric	The default inter-trial interval in ms. The default value if none is specified is 0ms.
experiment_width	numeric	The desired width of the jsPsych container in pixels. If left undefined, the width will be 100% of the display element. Usually this is the `<body>` element, and the width will be 100% of the screen size.
minimum_valid_rt	numeric	The minimum valid response time for key presses during the experiment. Any key press response time that is less than this value will be treated as invalid and ignored. Note that this parameter only applies to keyboard responses, and not to other response types such as buttons and sliders. The default value is 0.
override_safe_mode	boolean	Running a jsPsych experiment directly in a web browser (e.g., by double clicking on a local HTML file) will load the page using the `file://` protocol. Some features of jsPsych don't work with this protocol. By default, when jsPsych detects that it's running on a page loaded via the `file://` protocol, it runs in safe mode, which automatically disables features that don't work in this context. Specifically, the use of Web Audio is disabled (audio will be played using HTML5 audio instead, even if `use_webaudio` is `true`) and video preloading is disabled. The `override_safe_mode` parameter defaults to `false`, but you can set it to `true` to force these features to operate under the `file://` protocol. In order for this to work, you will need to disable web security (CORS) features in your browser - this is safe to do if you know what you are doing. Note that this parameter has no effect when you are running the experiment on a web server, because the page will be loaded via the `http://` or `https://` protocol.
case_sensitive_responses	boolean	If `true`, then jsPsych will make a distinction between uppercase and lowercase keys when evaluating keyboard responses, e.g. "A" (uppercase) will not be recognized as a valid response if the trial only accepts "a" (lowercase). If false, then jsPsych will not make a distinction between uppercase and lowercase keyboard responses, e.g. both "a" and "A" responses will be valid when the trial's key choice parameter is "a". Setting this parameter to false is useful if you want key responses to be treated the same way when CapsLock is turned on or the Shift key is held down. The default value is `false`.
extensions	array	Array containing information about one or more jsPsych extensions that are used during the experiment. Each extension should be specified as an object with `type` (required), which is the name of the extension, and `params` (optional), which is an object containing any parameter-value pairs to be passed to the extension's `initialize` function. Default value is an empty array.

Return value¶

Returns a jsPsych instance, which all jsPsych methods on this page are called on. Therefore it is not possible to call any of the jsPsych methods listed on this page until this initJsPsych function is called and a jsPsych instance is created.

Description¶

This function initializes jsPsych with the specified experiment settings.

Example¶

var jsPsych = initJsPsych({
  on_finish: function() {
    jsPsych.data.displayData();
  }, 
  show_progress_bar: true,
  default_iti: 500
});

For more examples, see the HTML files in the examples folder.

jsPsych.abortCurrentTimeline¶

jsPsych.abortCurrentTimeline()

Parameters¶

None.

Return value¶

None.

Description¶

Ends the current timeline. If timelines are nested, then only the timeline that contains the current trial is ended.

Example¶

Abort timeline if a particular key is pressed¶

var jsPsych = initJsPsych({
  on_finish: function() {
    jsPsych.data.displayData();
  }
});

var images = [
  "img/1.gif", "img/2.gif", "img/3.gif", "img/4.gif",
  "img/5.gif", "img/6.gif", "img/7.gif", "img/8.gif",
  "img/9.gif", "img/10.gif"
];

var trials = [];
for (var i = 0; i < images.length; i++) {
  trials.push({
    stimulus: images[i]
  });
}

var block = {
  type: jsPsychImageKeyboardResponse,
  choices: ['y', 'n'], 
  prompt: '<p>Press "y" to Continue. Press "n" to end this node of the experiment.</p>',
  on_finish: function(data) {
    if (jsPsych.pluginAPI.compareKeys(data.response, 'n')) {
      jsPsych.abortCurrentTimeline();
    }
  },
  timeline: trials
}

var after_block = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: '<p>The next node</p>'
}

jsPsych.run([block, after_block]);

jsPsych.abortExperiment¶

jsPsych.abortExperiment(message, data)

Parameters¶

Parameter	Type	Description
message	string	A message to display on the screen after the experiment is over. Can include HTML formatting.
data	object	An optional object of key-value pairs to store as data in the final trial of the experiment.

Return value¶

None.

Description¶

Ends the experiment, skipping all remaining trials. If the on_finish event handler for jsPsych returns a Promise then the message will not be displayed until the promise is resolved.

Example¶

End the experiment if a particular response is given¶

var trial = {
  type: jsPsychImageKeyboardResponse,
  stimulus: 'image1.jpg',
  choices: ['y', 'n'],
  prompt: '<p>Press "y" to Continue. Press "n" to end the experiment</p>',
  on_finish: function(data){
    if(jsPsych.pluginAPI.compareKeys(data.response, "n")){
      jsPsych.abortExperiment('The experiment was ended by pressing "n".');
    }
  }
}

jsPsych.abortTimelineByName¶

jsPsych.abortTimelineByName()

Parameters¶

Parameter	Type	Description
name	string	The name of the timeline to abort.

Return value¶

None.

Description¶

Ends the currently active timeline that matches the name parameter. This can be used to control which level is aborted in a nested timeline structure.

Example¶

Abort a procedure if an incorrect response is given.¶

const fixation = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: '<p>+</p>',
  choices: "NO_KEYS",
  trial_duration: 1000
}

const test = {
  type: jsPsychImageKeyboardResponse,
  stimulus: jsPsych.timelineVariable('stimulus'),
  choices: ['y', 'n'],
  on_finish: function(data){
    if(jsPsych.pluginAPI.compareKeys(data.response, "n")){
      jsPsych.abortTimelineByName('memory_test');
    }
  }
}

const memoryResponseProcedure = {
  timeline: [fixation, test]
}

// the variable `encode` is not shown, but imagine a trial that displays
// some stimulus to remember.
const memoryEncodeProcedure = {
  timeline: [fixation, encode]
}

const memoryTestProcedure = {
  timeline: [memoryEncodeProcedure, memoryResponseProcedure]
  name: 'memory_test',
  timeline_variables: [
    {stimulus: 'image1.png'},
    {stimulus: 'image2.png'},
    {stimulus: 'image3.png'},
    {stimulus: 'image4.png'}
  ]
}

jsPsych.evaluateTimelineVariable¶

jsPsych.evaluateTimelineVariable(variable_name)

Parameters¶

Parameter	Type	Description
variable_name	string	The name of the variable to evaluate.

Return value¶

Returns the current value of the corresponding timeline variable.

Description¶

Unlike jsPsych.timelineVariable(), evaluateTimelineVariable() immediately returns the current value of the timeline variable. It should be used whenever you are in a context where immediate evaluation is appropriate. For example, if you referencing a timeline variable within a function, immediate evaluation is usually correct.

Examples¶

Invoking timeline variables immediately in a function¶

const trial = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: function(){
    return `<img style='width:100px; height:100px;' src='${jsPsych.evaluateTimelineVariable('image')}'></img>`;
  }
}

const procedure = {
  timeline: [trial],
  timeline_variables: [
    {image: 'face1.png'},
    {image: 'face2.png'},
    {image: 'face3.png'},
    {image: 'face4.png'}
  ]
}

jsPsych.finishTrial¶

jsPsych.finishTrial(data)

Parameters¶

Parameter	Type	Description
data	object	The data to store for the trial.

Return value¶

Returns nothing.

Description¶

This method tells jsPsych that the current trial is over. It is used in all of the plugins to end the current trial. When the trial ends, a few things happen:

The data is stored using jsPsych.data.write()
The on_finish callback function is executed for the trial
The on_trial_finish callback function is executed
The display element is cleared, and any timeouts that are pending are cleared.
The progress bar is updated if it is being displayed
The experiment ends if the trial is the last one (and the on_finish callback function is executed).
The next trial, if one exists, is started.

Example¶

// this code would be in a plugin
jsPsych.finishTrial({correct_response: true});

jsPsych.getCitations¶

jsPsych.getCitations(plugins, format)

Parameters¶

Parameter	Type	Description
plugins	array	Array containing list of plugins/extensions by name.
format	string	Output citation format ("apa"

Return value¶

String of generated citations in the specified format for the jsPsych library, followed by that for each input plugin/extension, separated with a "\n" character.

Description¶

Get citations in a specified format for the jsPsych library and input list of plugins/extensions, usually those used within an experiment.

Example¶

// in browser console
jsPsych.getCitations() // prints citation for jsPsych library in APA format
jsPsych.getCitations([TestPlugin], "bibtex") // prints citation for jsPsych library and TestPlugin (if different) in BibTex format

jsPsych.getCurrentTrial¶

jsPsych.getCurrentTrial()

Parameters¶

None.

Return value¶

Returns the object describing the current trial. The object will contain all of the parameters associated with the current trial.

Description¶

Get a description of the current trial.

Example¶

var trial = jsPsych.getCurrentTrial();
console.log('The current trial is using the '+trial.type+' plugin');

jsPsych.getDisplayElement¶

jsPsych.getDisplayElement()

Parameters¶

None.

Return value¶

Returns the HTML DOM element used for displaying the experiment.

Description¶

Get the DOM element that displays the experiment.

Example¶

var el = jsPsych.getDisplayElement();

// hide the jsPsych display
el.style.visibility = 'hidden';

jsPsych.getInitSettings¶

jsPsych.getInitSettings()

Parameters¶

None

Return value¶

Returns the settings object used to initialize the experiment.

Description¶

Gets the object containing the settings for the current experiment.

Example¶

var settings = jsPsych.getInitSettings();

// check the experiment structure
console.log(JSON.stringify(settings.timeline));

jsPsych.getProgress¶

jsPsych.getProgress()

Parameters¶

None.

Return value¶

Returns an object with the following properties:

Property	Type	Description
total_trials	numeric	Indicates the number of trials in the experiment. Note that this does not count possible loops or skipped trials due to conditional statements.
current_trial_global	numeric	Returns the trial index of the current trial in a global scope. Every trial will increase this count by 1.
percent_complete	numeric	Estimates the percent of the experiment that is complete. Works as expected for experiments without conditional or looping timelines. For complex timelines, the percent is an approximation.

Description¶

This method returns information about the length of the experiment and the participant's current location in the experiment timeline.

Example¶

var progress = jsPsych.getProgress();
alert('You have completed approximately '+progress.percent_complete+'% of the experiment');

jsPsych.getStartTime¶

jsPsych.getStartTime()

Parameters¶

None.

Return value¶

Returns a Date object indicating when the experiment began.

Description¶

Get the time that the experiment began.

Example¶

var start_time = jsPsych.getStartTime();

jsPsych.getTotalTime¶

jsPsych.getTotalTime()

Parameters¶

None.

Return value¶

Returns a numeric value indicating the number of milliseconds since jsPsych.run was called.

Description¶

Gets the total time the participant has been in the experiment.

Example¶

var time = jsPsych.getTotalTime();
console.log(time);

jsPsych.pauseExperiment¶

jsPsych.pauseExperiment()

Parameters¶

None.

Return value¶

None.

Description¶

Pauses the experiment. The experiment will finish the current trial, but will not execute any additional trials until jsPsych.resumeExperiment() is called.

Example¶

var trial = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: 'Press p to take a 30 second break. Otherwise, press c to continue immediately.',
  choices: ['p', 'c'],
  on_finish: function(data){
    if (jsPsych.pluginAPI.compareKeys(data.response, "p")) { 
      jsPsych.pauseExperiment();
      setTimeout(jsPsych.resumeExperiment, 30000);
    }
  }
}

jsPsych.resumeExperiment¶

jsPsych.resumeExperiment()

Parameters¶

None.

Return value¶

None.

Description¶

Resumes the experiment after a call to jsPsych.pauseExperiment(). If the post trial delay (post_trial_gap) has not yet been reached, then the experiment will not continue until the delay is finished. For example, if post_trial_gap was 10,000ms and jsPsych.resumeExperiment() was called 6,000ms after the previous trial finished, then the experiment would not continue for another 4,000ms.

Example¶

var trial = {
  type: jsPsychHtmlKeyboardResponse,
  stimulus: 'Press p to take a 30 second break. Otherwise, press c to continue immediately.',
  choices: ['p','c'],
  on_finish: function(data){
    if(jsPsych.pluginAPI.compareKeys(data.response, "p")) { 
      jsPsych.pauseExperiment();
      setTimeout(jsPsych.resumeExperiment, 30000);
    }
  }
}

jsPsych.run¶

jsPsych.run(timeline)

Parameters¶

Parameter	Type	Description
timeline	array	An array containing the objects that describe the experiment timeline. See Creating an Experiment: The Timeline.

Return value¶

None.

Description¶

Start the jsPsych experiment with the specified timeline.

Example¶

var timeline = [trial1, trial2, trial3];

jsPsych.run(timeline);

jsPsych.timelineVariable¶

jsPsych.timelineVariable(variable)

Parameters¶

Parameter	Type	Description
variable	string	Name of the timeline variable

Return value¶

Returns a placeholder object that jsPsych uses to evaluate the timeline variable when the trial runs.

Description¶

Timeline variables are a powerful technique for generating experiments with repetitive procedures but different parameter values. This function fetches the current value of a particular timeline variable. It must be used in conjunction with a timeline that has timeline variables. See the timeline variable section for details.

Examples¶

Use as a parameter for a trial¶

var trial = {
  type: jsPsychImageKeyboardResponse,
  stimulus: jsPsych.timelineVariable('image')
}

var procedure = {
  timeline: [trial],
  timeline_variables: [
    {image: 'face1.png'},
    {image: 'face2.png'},
    {image: 'face3.png'},
    {image: 'face4.png'}
  ]
}

jsPsych.version¶

jsPsych.version()

Parameters¶

None.

Return value¶

Returns the version number as a string.

Description¶

Gets the version of jsPsych.

Example¶

var version = jsPsych.version();
console.log(version);