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Calling commands

Elements contain content that can be manipulated with commands.

Types of commands

There are three main types of commands:

Element commands can be further categorized as an action command or test command:

  • Element commands
    • Action command: Directly manipulates an element
    • Test command (PennController equivalent of a conditional statement): Runs a test on an element, and executes different code blocks depending on the success or failure of the test.

This tutorial uses the term “command” as shorthand for “action command”. If a test, global or special command is intended, the term “test command”, “global command”, or “special command” will be used.


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Command syntax

To call a command, the command:

  • Must be surrounded with . and (), for example .print(). The surrounding . and () are dropped when referring to a command in prose outside of a code block, for example “the print command”.
  • Must be called on an element, in other words on an instance of the newX or getX functions. Multiple commands can be called on a single element; commands are evaluated in the order in which they are called.

Call each command on an indented new line for maximum readability:


    newX("ELEMENT_1", ...)
    newX("ELEMENT_2", ...)

However, it is also valid to call multiple commands on a single line:


  newX("ELEMENT_1", ...).COMMAND_1().COMMAND_2().COMMAND_3()
  newX("ELEMENT_2", ...).COMMAND_4()

To learn about calling other types of commands, read the Commands documentation page.

Calling a command


  • Call the play command on the "fish-audio" Audio to start audio playback.
  • Call the print command on the "fish-sentence" Text and "fish-plural" Image to print them to the screen.

@// Type code below this line.
@// Remove command prefix
@// Experimental trial
@    newAudio("fish-audio", "2fishRoundTank.mp3
+        .play()
@    ,
@    newText("fish-sentence", "The fish swim in a tank which is perfectly round.")
+        .print()
@    ,
@    newImage("fish-plural", "2fishRoundTank.png")
+        .print()

Click Save and test in the script editor to run the experiment.

Evaluating an experiment script

You may be surprised by the results. When you run the experiment, you hear the audio file, but only see the message "The results were successfully sent to the server. Thanks!".

PennController executes experiment scripts sequentially. According to the current experiment script, the execution is as follows:

  1. Remove the command prefix for all commands.
  2. Start the "experimental-trial" trial.
  3. Create the "fish-audioAudio and play it.
  4. Create the "fish-sentence" Text and print it.
  5. Create the "fish-plural" Image and print it.
  6. End the "experimental-trial" trial.
  7. (Default): Send experiment results to the server, the PCIbex Farm. An experiment’s results are logged in its project page’s Results folder.
    • PennController automatically sends results after all other trials have ended. To control when results are sent, see the global command SendResults.
    • PennController automatically logs when a trial starts and ends. To log other information, see 6. Logging data.

As the "fish-audio" Audio is playing, all of the other commands are executed. When there are no more commands to execute, the trial ends. When there are no more trials to start, the experiment sends its results and ends. And all of this occurred within a few milliseconds!