How to use the vega-scale.scale function in vega-scale

export default function(scale, p0, p1, count, group) {
  scale = getScale(scale, (group || this).context);

  const gradient = Gradient(p0, p1);

  let stops = scale.domain(),
      min = stops[0],
      max = peek(stops),
      fraction = identity

  if (!(max - min)) {
    // expand scale if domain has zero span, fix #1479
    scale = (scale.interpolator
      ? get('sequential')().interpolator(scale.interpolator())
      : get('linear')().interpolate(scale.interpolate()).range(scale.range())
    ).domain([min=0, max=1]);
  } else {
    fraction = scaleFraction(scale, min, max);
  }

  if (scale.ticks) {
    stops = scale.ticks(+count || 15);
    if (min !== stops[0]) stops.unshift(min);
    if (max !== peek(stops)) stops.push(max);
  }

  stops.forEach(_ => gradient.stop(fraction(_), scale(_)));

  return gradient;
}

export default function(scale, p0, p1, count, group) {
  scale = getScale(scale, (group || this).context);

  const gradient = Gradient(p0, p1);

  let stops = scale.domain(),
      min = stops[0],
      max = peek(stops),
      fraction = identity

  if (!(max - min)) {
    // expand scale if domain has zero span, fix #1479
    scale = (scale.interpolator
      ? get('sequential')().interpolator(scale.interpolator())
      : get('linear')().interpolate(scale.interpolate()).range(scale.range())
    ).domain([min=0, max=1]);
  } else {
    fraction = scaleFraction(scale, min, max);
  }

  if (scale.ticks) {
    stops = scale.ticks(+count || 15);
    if (min !== stops[0]) stops.unshift(min);
    if (max !== peek(stops)) stops.push(max);
  }

  stops.forEach(_ => gradient.stop(fraction(_), scale(_)));

  return gradient;
}

if (!(mod || pulse.changed(pulse.ADD_REM) || Params.some(modp))) return;

  var data = pulse.materialize(pulse.SOURCE).source,
      layout = this.value,
      as = _.as || Output,
      fontSize = _.fontSize || 14,
      range;

  isFunction(fontSize)
    ? (range = _.fontSizeRange)
    : (fontSize = constant(fontSize));

  // create font size scaling function as needed
  if (range) {
    var fsize = fontSize,
        sizeScale = scale('sqrt')()
          .domain(extent(fsize, data))
          .range(range);
    fontSize = function(x) { return sizeScale(fsize(x)); };
  }

  data.forEach(function(t) {
    t[as[0]] = NaN;
    t[as[1]] = NaN;
    t[as[3]] = 0;
  });

  // configure layout
  var words = layout
    .words(data)
    .text(_.text)
    .size(_.size || [500, 500])

prototype.transform = function(_, pulse) {
  var df = pulse.dataflow,
      scale = this.value,
      key = scaleKey(_);

  if (!scale || key !== scale.type) {
    this.value = scale = getScale(key)();
  }

  for (key in _) if (!SKIP[key]) {
    // padding is a scale property for band/point but not others
    if (key === 'padding' && includePad(scale.type)) continue;
    // invoke scale property setter, raise warning if not found
    isFunction(scale[key])
      ? scale[key](_[key])
      : df.warn('Unsupported scale property: ' + key);
  }

  configureRange(scale, _,
    configureBins(scale, _, configureDomain(scale, _, df))
  );

  return pulse.fork(pulse.NO_SOURCE | pulse.NO_FIELDS);