area.defined()

area.defined([defined])

If defined is specified, sets the defined accessor to the specified function or boolean and returns this area generator. If defined is not specified, returns the current defined accessor, which defaults to:

function defined() {
  return true;
}

The default accessor thus assumes that the input data is always defined. When an area is generated, the defined accessor will be invoked for each element in the input data array, being passed the element d, the index i, and the array data as three arguments. If the given element is defined (i.e., if the defined accessor returns a truthy value for this element), the x0, x1, y0 and y1 accessors will subsequently be evaluated and the point will be added to the current area segment. Otherwise, the element will be skipped, the current area segment will be ended, and a new area segment will be generated for the next defined point. As a result, the generated area may have several discrete segments. For example:

Note that if an area segment consists of only a single point, it may appear invisible unless rendered with rounded or square line caps. In addition, some curves such as curveCardinalOpen only render a visible segment if it contains multiple points.