Chart.js/docs/scripts/log2.js

import {Scale, LinearScale} from 'chart.js';

export default class Log2Axis extends Scale {
  constructor(cfg) {
    super(cfg);
    this._startValue = undefined;
    this._valueRange = 0;
  }

  parse(raw, index) {
    const value = LinearScale.prototype.parse.apply(this, [raw, index]);
    return isFinite(value) && value > 0 ? value : null;
  }

  determineDataLimits() {
    const {min, max} = this.getMinMax(true);
    this.min = isFinite(min) ? Math.max(0, min) : null;
    this.max = isFinite(max) ? Math.max(0, max) : null;
  }

  buildTicks() {
    const ticks = [];

    let power = Math.floor(Math.log2(this.min || 1));
    let maxPower = Math.ceil(Math.log2(this.max || 2));
    while (power <= maxPower) {
      ticks.push({value: Math.pow(2, power)});
      power += 1;
    }

    this.min = ticks[0].value;
    this.max = ticks[ticks.length - 1].value;
    return ticks;
  }

  /**
   * @protected
   */
  configure() {
    const start = this.min;

    super.configure();

    this._startValue = Math.log2(start);
    this._valueRange = Math.log2(this.max) - Math.log2(start);
  }

  getPixelForValue(value) {
    if (value === undefined || value === 0) {
      value = this.min;
    }

    return this.getPixelForDecimal(value === this.min ? 0
      : (Math.log2(value) - this._startValue) / this._valueRange);
  }

  getValueForPixel(pixel) {
    const decimal = this.getDecimalForPixel(pixel);
    return Math.pow(2, this._startValue + decimal * this._valueRange);
  }
}

Log2Axis.id = 'log2';
Log2Axis.defaults = {};

// The derived axis is registered like this:
// Chart.register(Log2Axis);