How to use the vis-util.convert function in vis-util

Range.prototype._applyRange = function(start, end) {
  var newStart = (start != null) ? util.convert(start, 'Date').valueOf() : this.start,
      newEnd   = (end != null)   ? util.convert(end, 'Date').valueOf()   : this.end,
      max = (this.options.max != null) ? util.convert(this.options.max, 'Date').valueOf() : null,
      min = (this.options.min != null) ? util.convert(this.options.min, 'Date').valueOf() : null,
      diff;

  // check for valid number
  if (isNaN(newStart) || newStart === null) {
    throw new Error('Invalid start "' + start + '"');
  }
  if (isNaN(newEnd) || newEnd === null) {
    throw new Error('Invalid end "' + end + '"');
  }

  // prevent end < start
  if (newEnd < newStart) {
    newEnd = newStart;

TimeAxis.prototype._repaintLabels = function () {
  var orientation = this.options.orientation.axis;

  // calculate range and step (step such that we have space for 7 characters per label)
  var start = util.convert(this.body.range.start, 'Number');
  var end = util.convert(this.body.range.end, 'Number');
  var timeLabelsize = this.body.util.toTime((this.props.minorCharWidth || 10) * this.options.maxMinorChars).valueOf();
  var minimumStep = timeLabelsize - DateUtil.getHiddenDurationBefore(this.options.moment, this.body.hiddenDates, this.body.range, timeLabelsize);
  minimumStep -= this.body.util.toTime(0).valueOf();

  var step = new TimeStep(new Date(start), new Date(end), minimumStep, this.body.hiddenDates, this.options);
  step.setMoment(this.options.moment);
  if (this.options.format) {
    step.setFormat(this.options.format);
  }
  if (this.options.timeAxis) {
    step.setScale(this.options.timeAxis);
  }
  this.step = step;

  // Move all DOM elements to a "redundant" list, where they

TimeAxis.prototype._repaintLabels = function () {
  var orientation = this.options.orientation.axis;

  // calculate range and step (step such that we have space for 7 characters per label)
  var start = util.convert(this.body.range.start, 'Number');
  var end = util.convert(this.body.range.end, 'Number');
  var timeLabelsize = this.body.util.toTime((this.props.minorCharWidth || 10) * this.options.maxMinorChars).valueOf();
  var minimumStep = timeLabelsize - DateUtil.getHiddenDurationBefore(this.options.moment, this.body.hiddenDates, this.body.range, timeLabelsize);
  minimumStep -= this.body.util.toTime(0).valueOf();

  var step = new TimeStep(new Date(start), new Date(end), minimumStep, this.body.hiddenDates, this.options);
  step.setMoment(this.options.moment);
  if (this.options.format) {
    step.setFormat(this.options.format);
  }
  if (this.options.timeAxis) {
    step.setScale(this.options.timeAxis);
  }
  this.step = step;

  // Move all DOM elements to a "redundant" list, where they
  // can be picked for re-use, and clear the lists with lines and texts.

Range.prototype._applyRange = function(start, end) {
  var newStart = (start != null) ? util.convert(start, 'Date').valueOf() : this.start,
      newEnd   = (end != null)   ? util.convert(end, 'Date').valueOf()   : this.end,
      max = (this.options.max != null) ? util.convert(this.options.max, 'Date').valueOf() : null,
      min = (this.options.min != null) ? util.convert(this.options.min, 'Date').valueOf() : null,
      diff;

  // check for valid number
  if (isNaN(newStart) || newStart === null) {
    throw new Error('Invalid start "' + start + '"');
  }
  if (isNaN(newEnd) || newEnd === null) {
    throw new Error('Invalid end "' + end + '"');
  }

  // prevent end < start
  if (newEnd < newStart) {
    newEnd = newStart;
  }

Range.prototype._applyRange = function(start, end) {
  var newStart = (start != null) ? util.convert(start, 'Date').valueOf() : this.start,
      newEnd   = (end != null)   ? util.convert(end, 'Date').valueOf()   : this.end,
      max = (this.options.max != null) ? util.convert(this.options.max, 'Date').valueOf() : null,
      min = (this.options.min != null) ? util.convert(this.options.min, 'Date').valueOf() : null,
      diff;

  // check for valid number
  if (isNaN(newStart) || newStart === null) {
    throw new Error('Invalid start "' + start + '"');
  }
  if (isNaN(newEnd) || newEnd === null) {
    throw new Error('Invalid end "' + end + '"');
  }

  // prevent end < start
  if (newEnd < newStart) {
    newEnd = newStart;
  }

  // prevent start < min

dataset.forEach(function (item) {
      var start = util.convert(item.start, 'Date').valueOf();
      var end   = util.convert(item.end != undefined ? item.end : item.start, 'Date').valueOf();
      if (min === null || start < min) {
        min = start;
      }
      if (max === null || end > max) {
        max = end;
      }
    });
  }

function getStart(item) {
  return util.convert(item.data.start, 'Date').valueOf()
}

function getEnd(item) {
  var end = item.data.end != undefined ? item.data.end : item.data.start;
  return util.convert(end, 'Date').valueOf();
}