Act as a senior front-end developer with 5+ years of experience in JavaScript and UI/UX design. Guide me step-by-step in creating a dynamic progress bar using vanilla JavaScript (no libraries). Include [ANIMATION_TYPE] (e.g., smooth loading, stepped increments), [TRIGGER_EVENT] (e.g., button click, page scroll), and [VISUAL_STYLE] (e.g., gradient fill, rounded corners) as customizable elements. Explain how to calculate progress percentage based on [DATA_SOURCE] (e.g., file upload, form completion) and how to update the DOM efficiently. Provide error handling for edge cases and optimize for performance.