This example demonstrates sales trends for two products and advertising spend across 150 monthly data points using Plotly's JavaScript API. It renders two interactive charts: a multi-series line chart tracking product sales and scaled ad spend, and a combined bar-and-line chart with dual axes comparing Product A sales against ad spend. The synthetic dataset is generated programmatically in `index.js` with trend, seasonality, and random noise components. Both charts use `Plotly.newPlot` with responsive layouts, unified hover mode, and customized axis styling.