Latest Torstein sync solution

by kzoon

HTML

<script src="https://code.highcharts.com/highcharts.js"></script>

<div id="container"></div>

CSS

#container {
    max-width: 800px;
    height: 400px;
    margin: 1em auto;
}

JavaScript

/**
 * Experimental Highcharts plugin to implement chart.alignThreshold option. This primary axis
 * will be computed first, then all following axes will be aligned to the threshold.
 * Author: Torstein Hønsi
 * Last revision: 2016-11-02
 */
(function (H) {
    var Axis = H.Axis,
        inArray = H.inArray,
        wrap = H.wrap;

    wrap(Axis.prototype, 'adjustTickAmount', function (proceed) {
        var chart = this.chart,
            primaryAxis = chart[this.coll][0],
            primaryThreshold,
            primaryIndex,
            index,
            newTickPos,
            threshold;

        // Find the index and return boolean result
        function isAligned(axis) {
            index = inArray(threshold, axis.tickPositions); // used in while-loop
            return axis.tickPositions.length === axis.tickAmount && index === primaryIndex;
        }

        if (chart.options.chart.alignThresholds && this !== primaryAxis) {
            primaryThreshold = (primaryAxis.series[0] && primaryAxis.series[0].options.threshold) || 0;
            threshold = (this.series[0] && this.series[0].options.threshold) || 0;

            primaryIndex = primaryAxis.tickPositions && inArray(primaryThreshold, primaryAxis.tickPositions);

            if (this.tickPositions && this.tickPositions.length &&
                    primaryIndex > 0 &&
                    primaryIndex < primaryAxis.tickPositions.length - 1 &&
                    this.tickAmount) {

                // Add tick positions to the top or bottom in order to align the threshold
                // to the primary axis threshold
                while (!isAligned(this)) {

                    if (index < primaryIndex) {
                        newTickPos = this.tickPositions[0] - this.tickInterval;
                        this.tickPositions.unshift(newTickPos);
                        this.min = newTickPos;
                    } else {
                        newTickPos =...