d3.interpolateObject()

d3.interpolateObject(a, b)

Returns an interpolator between the two objects a and b. Internally, an object template is created that has the same properties as b. For each property in b, if there exists a corresponding property in a, a generic interpolator is created for the two elements using interpolate. If there is no such property, the static value from b is used in the template. Then, for the given parameter t, the template's embedded interpolators are evaluated and the updated object template is then returned.

For example, if a is the object {x: 0, y: 1} and b is the object {x: 1, y: 10, z: 100}, the result of the interpolator for t = 0.5 is the object {x: 0.5, y: 5.5, z: 100}.

Object interpolation is particularly useful for dataspace interpolation, where data is interpolated rather than attribute values. For example, you can interpolate an object which describes an arc in a pie chart, and then use d3.svg.arc to compute the new SVG path data.

Note: no defensive copy of the template object is created; modifications of the returned object may adversely affect subsequent evaluation of the interpolator. No copy is made for performance reasons; interpolators are often part of the inner loop of animated transitions.