How to use the vega-util.inherits function in vega-util

import {Item, GroupItem} from 'vega-scenegraph';
import {inherits} from 'vega-util';

/**
 * Bind scenegraph items to a scenegraph mark instance.
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {object} params.markdef - The mark definition for creating the mark.
 *   This is an object of legal scenegraph mark properties which *must* include
 *   the 'marktype' property.
 */
export default function Mark(params) {
  Transform.call(this, null, params);
}

var prototype = inherits(Mark, Transform);

prototype.transform = function(_, pulse) {
  var mark = this.value;

  // acquire mark on first invocation, bind context and group
  if (!mark) {
    mark = pulse.dataflow.scenegraph().mark(_.markdef, lookup(_), _.index);
    mark.group.context = _.context;
    if (!_.context.group) _.context.group = mark.group;
    mark.source = this.source; // point to upstream collector
    mark.clip = _.clip;
    mark.interactive = _.interactive;
    this.value = mark;
  }

  // initialize entering items

* @param {function(object): *} params.key - The key field to facet by.
 */
export default function Facet(params) {
  Transform.call(this, {}, params);
  this._keys = fastmap(); // cache previously calculated key values

  // keep track of active subflows, use as targets array for listeners
  // this allows us to limit propagation to only updated subflows
  var a = this._targets = [];
  a.active = 0;
  a.forEach = function(f) {
    for (var i=0, n=a.active; i

/**
 * Generates data tuples using a provided generator function.
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {function(Parameters): object} params.generator - A tuple generator
 *   function. This function is given the operator parameters as input.
 *   Changes to any additional parameters will not trigger re-calculation
 *   of previously generated tuples. Only future tuples are affected.
 * @param {number} params.size - The number of tuples to produce.
 */
export default function Generate(params) {
  Transform.call(this, [], params);
}

var prototype = inherits(Generate, Transform);

prototype.transform = function(_, pulse) {
  var data = this.value,
      out = pulse.fork(pulse.ALL),
      num = _.size - data.length,
      gen = _.generator,
      add, rem, t;

  if (num > 0) {
    // need more tuples, generate and add
    for (add=[]; --num >= 0;) {
      add.push(t = ingest(gen(_)));
      data.push(t);
    }
    out.add = out.add.length
      ? out.materialize(out.ADD).add.concat(add)

Transform.call(this, Bitmaps(), params);
  this._indices = null;
  this._dims = null;
}

CrossFilter.Definition = {
  "type": "CrossFilter",
  "metadata": {},
  "params": [
    { "name": "fields", "type": "field", "array": true, "required": true },
    { "name": "query", "type": "array", "array": true, "required": true,
      "content": {"type": "number", "array": true, "length": 2} }
  ]
};

var prototype = inherits(CrossFilter, Transform);

prototype.transform = function(_, pulse) {
  if (!this._dims) {
    return this.init(_, pulse);
  } else {
    var init = _.modified('fields')
          || _.fields.some(function(f) { return pulse.modified(f.fields); });

    return init
      ? this.reinit(_, pulse)
      : this.eval(_, pulse);
  }
};

prototype.init = function(_, pulse) {
  var fields = _.fields,

import Operator from '../Operator';
import {inherits, key} from 'vega-util';

/**
 * Generates a key function.
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {Array} params.fields - The field name(s) for the key function.
 */
export default function Key(params) {
  Operator.call(this, null, update, params);
}

inherits(Key, Operator);

function update(_) {
  return (this.value && !_.modified()) ? this.value : key(_.fields);
}

"params": [
    { "name": "size", "type": "number", "array": true, "length": 2 },
    { "name": "font", "type": "string", "expr": true, "default": "sans-serif" },
    { "name": "fontStyle", "type": "string", "expr": true, "default": "normal" },
    { "name": "fontWeight", "type": "string", "expr": true, "default": "normal" },
    { "name": "fontSize", "type": "number", "expr": true, "default": 14 },
    { "name": "fontSizeRange", "type": "number", "array": "nullable", "default": [10, 50] },
    { "name": "rotate", "type": "number", "expr": true, "default": 0 },
    { "name": "text", "type": "field" },
    { "name": "spiral", "type": "string", "values": ["archimedean", "rectangular"] },
    { "name": "padding", "type": "number", "expr": true },
    { "name": "as", "type": "string", "array": true, "length": 7, "default": Output }
  ]
};

var prototype = inherits(Wordcloud, Transform);

prototype.transform = function(_, pulse) {
  if (_.size && !(_.size[0] && _.size[1])) {
    error('Wordcloud size dimensions must be non-zero.');
  }

  function modp(param) {
    var p = _[param];
    return isFunction(p) && pulse.modified(p.fields);
  }

  var mod = _.modified();
  if (!(mod || pulse.changed(pulse.ADD_REM) || Params.some(modp))) return;

  var data = pulse.materialize(pulse.SOURCE).source,
      layout = this.value,

/**
 * Extracts an array of values. Assumes the source data has already been
 * reduced as needed (e.g., by an upstream Aggregate transform).
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {function(object): *} params.field - The domain field to extract.
 * @param {function(*,*): number} [params.sort] - An optional
 *   comparator function for sorting the values. The comparator will be
 *   applied to backing tuples prior to value extraction.
 */
export default function Values(params) {
  Transform.call(this, null, params);
}

var prototype = inherits(Values, Transform);

prototype.transform = function(_, pulse) {
  var run = !this.value
    || _.modified('field')
    || _.modified('sort')
    || pulse.changed()
    || (_.sort && pulse.modified(_.sort.fields));

  if (run) {
    this.value = (_.sort
      ? pulse.source.slice().sort(stableCompare(_.sort))
      : pulse.source).map(_.field);
  }
};

import {accessorName, error, inherits} from 'vega-util';

/**
 * Extend tuples by joining them with values from a lookup table.
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {Map} params.index - The lookup table map.
 * @param {Array} params.as - Output field names for each lookup value.
 * @param {*} [params.default] - A default value to use if lookup fails.
 */
export default function Lookup(params) {
  Transform.call(this, {}, params);
}

var prototype = inherits(Lookup, Transform);

prototype.transform = function(_, pulse) {
  var out = pulse,
      as = _.as,
      keys = _.fields,
      index = _.index,
      values = _.values,
      defaultValue = _.default==null ? null : _.default,
      reset = _.modified(),
      flag = reset ? pulse.SOURCE : pulse.ADD,
      n = keys.length,
      set, m, mods;

  if (values) {
    m = values.length;

/**
 * Extracts an array of values. Assumes the source data has already been
 * reduced as needed (e.g., by an upstream Aggregate transform).
 * @constructor
 * @param {object} params - The parameters for this operator.
 * @param {function(object): *} params.field - The domain field to extract.
 * @param {function(*,*): number} [params.sort] - An optional
 *   comparator function for sorting the values. The comparator will be
 *   applied to backing tuples prior to value extraction.
 */
export default function Values(params) {
  Transform.call(this, null, params);
}

var prototype = inherits(Values, Transform);

prototype.transform = function(_, pulse) {
  var run = !this.value
    || _.modified('field')
    || _.modified('sort')
    || pulse.changed()
    || (_.sort && pulse.modified(_.sort.fields));

  if (run) {
    this.value = (_.sort
      ? pulse.source.slice().sort(_.sort)
      : pulse.source).map(_.field);
  }
};

}

Partition.Definition = {
  "type": "Partition",
  "metadata": {"tree": true, "modifies": true},
  "params": [
    { "name": "field", "type": "field" },
    { "name": "sort", "type": "compare" },
    { "name": "padding", "type": "number", "default": 0 },
    { "name": "round", "type": "boolean", "default": false },
    { "name": "size", "type": "number", "array": true, "length": 2 },
    { "name": "as", "type": "string", "array": true, "length": Output.length, "default": Output }
  ]
};

var prototype = inherits(Partition, HierarchyLayout);

prototype.layout = partition;

prototype.params = ['size', 'round', 'padding'];

prototype.fields = Output;