This example compares eight different d3 v4 curve interpolation methods (linear, step, basis, cardinal, monotone, and Catmull-Rom variants) on a shared time-series of stock closing prices. Each curve is drawn as an SVG path, and clicking a legend label toggles its opacity via `d3.select(...).transition().duration(100)`. The visualization uses `d3.line()` with a `.curve()` method to generate the paths, `d3.axisBottom` and `d3.axisLeft` for axes, and `d3.scaleOrdinal` with `d3.schemeCategory10` for colors. Data is loaded from a CSV file with `d3.csv`.