Debugging and data checks

Start with the first error

Open the Console, clear old messages, refresh once, and read the first error. Later errors often follow from it. Keep the Network panel available for missing scripts and images. Change one thing at a time and rerun the smallest relevant case.

Symptom	Likely cause	Check
`initJsPsych is not defined`	Core script missing or loaded too late	HTML script path and order
Plugin variable undefined	Plugin not loaded or wrong global name	Match script filename with documented plugin class
Page shows `[object Object]`	v8 placeholder inserted inside a function	Use `evaluateTimelineVariable` inside the function
Every item looks identical	Literal text or parameter computed too early	Dynamic stimulus function and current item
`Unexpected token`	Missing comma, quote, or brace	First indicated line plus the preceding line
Image missing	Wrong path or filename case	Open asset URL directly; inspect preload result
Keys do nothing	Wrong allowed keys, page lacks focus, deadline ended	Click page, inspect choices, try again
Correct answer marked wrong	Key mapping, type mismatch, or wrong answer key	Hand-score one saved row
Practice never ends	Cumulative data or unbounded loop	Current attempt filter and maximum attempts
`NaN` on summary	Empty eligible RT set	Return N/A if no eligible trials
Results disappear on refresh	Browser memory was not saved	Use download controls before refresh
JATOS page remains local	Wrong entry HTML or not launched from runner	Use generated `index-jatos.html` through JATOS

Four-minute data audit

Run a short pilot with one correct answer, one wrong answer, and one deliberate timeout.
Filter to the task and block. Count trials independently from the stimulus list.
For one row, reconstruct the expected response from the displayed stimulus and mapping. Do not use the saved correct_response field as the sole source of truth.
Check that the omission has response: null, rt: null, and correct: false where accuracy is scored.
Confirm the accuracy denominator includes all test trials. Confirm RT includes only correct, finite responses.
Download CSV and JSON. Open both; check the final trial is present. Nested pointer data is easier to inspect in JSON.

Bug report template

Page/path and browser:
Action I took:
Expected behavior:
Actual behavior:
First Console error (copy text):
Smallest example that reproduces it:
One change I already tested:

A useful bug report describes an observation, not merely “it doesn’t work.” Keep identifying participant information out of examples.