Return a javascript function that checks a data value

fn_data_condition(expr, trials_back = 1)



An expression to be evaluated within the jsPsych data store


The number of trials before the present one for which to query the data


A javascript function


The fn_data_condition() function creates a javascript function that can query the jsPsych data store and evaluate the expression expr within the data store. It is (at present) very limited, and can only query the data store for a single trial (i.e., a single row in the data set). By default it queries the most recent trial (trials_back = 1) but this behaviour can be modified.

The intention behind this function is that it be used in conjunction with functions such as display_if() and display_while() that require a javascript function that will evaluate to true or false, in order to determine whether to continue the while loop or whether the if condition holds.

As an example, one might set fn_data_condition(button_pressed == "0") when calling display_if(). If the participant had pressed button "0" on the previous trial, then the timeline in question will be executed. Otherwise it is not.

Note that this function is a work in progress and will likely change in future versions in order to allow more flexibility.