d3/src/core/array.js

A small, free JavaScript library for manipulating documents based on data.

var d3_arraySubclass = [].__proto__?

// Until ECMAScript supports array subclassing, prototype injection works well.
function(array, prototype) {
  array.__proto__ = prototype;
}:

// And if your browser doesn't support __proto__, we'll use direct extension.
function(array, prototype) {
  for (var property in prototype) array[property] = prototype[property];
};