source: node_modules/d3-scale/src/pow.js

import {linearish} from "./linear.js";
import {copy, identity, transformer} from "./continuous.js";
import {initRange} from "./init.js";

function transformPow(exponent) {
  return function(x) {
    return x < 0 ? -Math.pow(-x, exponent) : Math.pow(x, exponent);
  };
}

function transformSqrt(x) {
  return x < 0 ? -Math.sqrt(-x) : Math.sqrt(x);
}

function transformSquare(x) {
  return x < 0 ? -x * x : x * x;
}

export function powish(transform) {
  var scale = transform(identity, identity),
      exponent = 1;

  function rescale() {
    return exponent === 1 ? transform(identity, identity)
        : exponent === 0.5 ? transform(transformSqrt, transformSquare)
        : transform(transformPow(exponent), transformPow(1 / exponent));
  }

  scale.exponent = function(_) {
    return arguments.length ? (exponent = +_, rescale()) : exponent;
  };

  return linearish(scale);
}

export default function pow() {
  var scale = powish(transformer());

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

  initRange.apply(scale, arguments);

  return scale;
}

export function sqrt() {
  return pow.apply(null, arguments).exponent(0.5);
}