function cursorFrom(rootData, keyPath, onChange) {
  if (arguments.length === 1) {
    keyPath = [];
  } else if (typeof keyPath === 'function') {
    onChange = keyPath;
    keyPath = [];
  } else {
    keyPath = valToKeyPath(keyPath);
  }
  return makeCursor(rootData, keyPath, onChange);
}
Cursor is expected to be required in a node or other CommonJS context:

    var Cursor = require('immutable/contrib/cursor');

If you wish to use it in the browser, please check out Browserify or WebPack!