selection.html()

selection.html([value])

If a value is specified, sets the inner HTML to the specified value on all selected elements, replacing any existing child elements. If the value is a constant, then all elements are given the same inner HTML; otherwise, if the value is a function, then the function is evaluated for each selected element, in order, being passed the current datum (d), the current index (i), and the current group (nodes), with this as the current DOM element. The function’s return value is then used to set each element’s inner HTML. A null value will clear the content.

If a value is not specified, returns the inner HTML for the first (non-null) element in the selection. This is generally useful only if you know the selection contains exactly one element.

Use selection.append or selection.insert instead to create data-driven content; this method is intended for when you want a little bit of HTML, say for rich formatting. Also, selection.html is only supported on HTML elements. SVG elements and other non-HTML elements do not support the innerHTML property, and thus are incompatible with selection.html. Consider using XMLSerializer to convert a DOM subtree to text. See also the innersvg polyfill, which provides a shim to support the innerHTML property on SVG elements.