site/node_modules/d3-scale/src/linear.js

import {ticks, tickIncrement} from "d3-array";
import continuous, {copy} from "./continuous.js";
import {initRange} from "./init.js";
import tickFormat from "./tickFormat.js";

export function linearish(scale) {
  var domain = scale.domain;

  scale.ticks = function(count) {
    var d = domain();
    return ticks(d[0], d[d.length - 1], count == null ? 10 : count);
  };

  scale.tickFormat = function(count, specifier) {
    var d = domain();
    return tickFormat(d[0], d[d.length - 1], count == null ? 10 : count, specifier);
  };

  scale.nice = function(count) {
    if (count == null) count = 10;

    var d = domain();
    var i0 = 0;
    var i1 = d.length - 1;
    var start = d[i0];
    var stop = d[i1];
    var prestep;
    var step;
    var maxIter = 10;

    if (stop < start) {
      step = start, start = stop, stop = step;
      step = i0, i0 = i1, i1 = step;
    }
    
    while (maxIter-- > 0) {
      step = tickIncrement(start, stop, count);
      if (step === prestep) {
        d[i0] = start
        d[i1] = stop
        return domain(d);
      } else if (step > 0) {
        start = Math.floor(start / step) * step;
        stop = Math.ceil(stop / step) * step;
      } else if (step < 0) {
        start = Math.ceil(start * step) / step;
        stop = Math.floor(stop * step) / step;
      } else {
        break;
      }
      prestep = step;
    }

    return scale;
  };

  return scale;
}

export default function linear() {
  var scale = continuous();

  scale.copy = function() {
    return copy(scale, linear());
  };

  initRange.apply(scale, arguments);

  return linearish(scale);
}