jspsych/jsPsych ? reverse-engineered prompt

Build me a browser based framework for running simple behavioral experiments in JavaScript.

I want researchers to be able to put together an experiment from reusable pieces, like showing text, images, audio, video, collecting key presses or button clicks, timing responses, and moving through a timeline of tasks. It should also support things like instructions screens, reaction time tasks, drag and drop style activities, and custom tasks when needed.

Please include a clean example experiment so someone can open it in a browser and see how it works, plus enough documentation that a beginner can get started quickly. Make it easy to run locally, easy to extend with new task types, and organized for sharing data from the experiment. If you need to check current docs or examples online while building it, go ahead.