In D3.js, custom reusable components can be created using the concept of a reusable chart pattern. This pattern involves creating a function that generates an SVG element, and then setting up methods for updating the component with new data.To create a custom reusable component in D3.js, start by defining a function that generates the SVG element and sets up initial properties. This function should include all the necessary elements for the chart, such as scales, axes, and shapes.