adds first pass at #883

jspsych.js

@@ -273,6 +273,9 @@ window.jsPsych = (function() {
     // of the DataCollection, for easy access and editing.
     var trial_data_values = trial_data.values()[0];
 
+    // about to execute lots of callbacks, so switch context.
+    jsPsych.internal.call_immediate = true;
+
     // handle callback at plugin level
     if (typeof current_trial.on_finish === 'function') {
       current_trial.on_finish(trial_data_values);
@@ -286,6 +289,9 @@ window.jsPsych = (function() {
     // data object that just went through the trial's finish handlers.
     opts.on_data_update(trial_data_values);
 
+    // done with callbacks
+    jsPsych.internal.call_immediate = false;
+
     // wait for iti
     if (typeof current_trial.post_trial_gap === null || typeof current_trial.post_trial_gap === 'undefined') {
       if (opts.default_iti > 0) {
@@ -326,8 +332,9 @@ window.jsPsych = (function() {
     return timeline.activeID();
   };
 
-  core.timelineVariable = function(varname, execute){
-    if(execute){
+  core.timelineVariable = function(varname, immediate){
+    if(typeof immediate == 'undefined'){ immediate = false; }
+    if(jsPsych.internal.call_immediate || immediate === true){
       return timeline.timelineVariable(varname);
     } else {
       return function() { return timeline.timelineVariable(varname); }
@@ -489,7 +496,9 @@ window.jsPsych = (function() {
         // check for conditonal function on nodes with timelines
         if (typeof timeline_parameters != 'undefined') {
           if (typeof timeline_parameters.conditional_function !== 'undefined') {
+            jsPsych.internal.call_immediate = true;
             var conditional_result = timeline_parameters.conditional_function();
+            jsPsych.internal.call_immediate = false;
             // if the conditional_function() returns false, then the timeline
             // doesn't run and is marked as complete.
             if (conditional_result == false) {
@@ -550,11 +559,14 @@ window.jsPsych = (function() {
 
         // if we're all done with the repetitions, check if there is a loop function.
         else if (typeof timeline_parameters.loop_function !== 'undefined') {
+          jsPsych.internal.call_immediate = true;
           if (timeline_parameters.loop_function(this.generatedData())) {
             this.reset();
+            jsPsych.internal.call_immediate = false;
             return parent_node.advance();
           } else {
             progress.done = true;
+            jsPsych.internal.call_immediate = false;
             return true;
           }
         }
@@ -871,6 +883,9 @@ window.jsPsych = (function() {
     // get default values for parameters
     setDefaultValues(trial);
 
+    // about to execute callbacks
+    jsPsych.internal.call_immediate = true;
+
     // call experiment wide callback
     opts.on_trial_start(trial);
 
@@ -892,6 +907,9 @@ window.jsPsych = (function() {
     if(typeof trial.on_load == 'function'){
       trial.on_load();
     }
+    
+    // done with callbacks
+    jsPsych.internal.call_immediate = false;
   }
 
   function evaluateTimelineVariables(trial){
@@ -911,6 +929,9 @@ window.jsPsych = (function() {
 
   function evaluateFunctionParameters(trial){
 
+    // set a flag so that jsPsych.timelineVariable() is immediately executed in this context
+    jsPsych.internal.call_immediate = true;
+
     // first, eval the trial type if it is a function
     // this lets users set the plugin type with a function
     if(typeof trial.type === 'function'){
@@ -949,6 +970,9 @@ window.jsPsych = (function() {
         }
       }
     }
+
+    // reset so jsPsych.timelineVariable() is no longer immediately executed
+    jsPsych.internal.call_immediate = false;
   }
 
   function setDefaultValues(trial){
@@ -1066,6 +1090,17 @@ window.jsPsych = (function() {
   return core;
 })();
 
+jsPsych.internal = (function() {
+  var module = {};
+
+  // this flag is used to determine whether we are in a scope where
+  // jsPsych.timelineVariable() should be executed immediately or
+  // whether it should return a function to access the variable later.
+  module.call_immediate = false;
+
+  return module;
+})();
+
 jsPsych.plugins = (function() {
 
   var module = {};

tests/jsPsych/timeline-variables.test.js

@@ -250,5 +250,31 @@ describe('timeline variables are correctly evaluated', function(){
 
   });
 
+  test('when used inside a function', function(){
+    var tvs = [
+      {x: 'foo'},
+      {x: 'bar'}
+    ]
+
+    var trial = {
+      type: 'html-keyboard-response',
+      stimulus: function(){
+        return jsPsych.timelineVariable('x');
+      }
+    }
+
+    var p = {
+      timeline: [trial],
+      timeline_variables: tvs
+    }
+
+    jsPsych.init({
+      timeline: [p]
+    })
+
+    expect(jsPsych.getDisplayElement().innerHTML).toMatch('foo');
+    utils.pressKey(32);
+    expect(jsPsych.getDisplayElement().innerHTML).toMatch('bar');
+  });
 
 })