Calculate the height for a specific width and aspect ratio with JavaScript

calcAspectRatioHeight.js

/**
 * Calculate the height for a specific width and aspect ratio.
 *
 * @param {Number} width The width used to generate a height for the aspect ratio.
 * @param {string} aspectRatio The aspect ratio with the ':' as a delimiter. Example: '16:9'.
 * @returns {Number} the height for the aspect ratio.
 */
export default function calcAspectRatioHeight(width = 100, aspectRatio = '16:9') {
  let y = String(aspectRatio); // make a copy of the aspect ratio.

  const errorMessage = `calcAspectRatioHeight() contains an invalid aspect ratio format of "${aspectRatio}"`;

  // If the aspect ratio is invalid use the default value of 16:9.
  if (!y || !y.includes(':')) {
    y = '16:9';
    // eslint-disable-next-line no-console
    console.log(errorMessage);
  }
  // Split the string between the delimiter in order to run the aspect ratio calculation.
  let [divisor, dividend] = y.split(':', 2);

  // Cast the divisor and dividend as integers.
  divisor = Number(divisor);
  dividend = Number(dividend);

  let quotient = dividend / divisor;

  // Check for empty values for quotient assignment and fallback to 16:9 otherwise.
  if ((!divisor || Number.isNaN(divisor)) || (!dividend || Number.isNaN(dividend))) {
    quotient = 9 / 16;
  }

  // In the case that the quotient is invalid or not a number, use the default aspect ratio.
  if (Number.isNaN(quotient)) {
    // eslint-disable-next-line no-console
    console.log(errorMessage);
    quotient = 9 / 16;
  }

  // Set the width as a number and fallback to 100 as a default.
  const x = width ? Number(width) : 100;

  return quotient * x;
}

/**
 * Set the following as a Jest test in an adjacent file. e.g. 'calcAspectRatioHeight.test.js'
 *
 * @jest-environment jsdom
 */
// import calcAspectRatioHeight from './calcAspectRatioHeight';

describe('Test function `calcAspectRatioHeight`.', () => {
  test('Should be 56.25 if no params are passed.', () => {
    expect(calcAspectRatioHeight()).toBe(56.25);
  });

  test('Should use default 16:9 aspect ratio if only width parameter is passed.', () => {
    expect(calcAspectRatioHeight(78)).toBe(43.875);
    expect(calcAspectRatioHeight(100)).toBe(56.25);
  });

  test('An aspect ratio should output the correct height calculation.', () => {
    expect(calcAspectRatioHeight(100, '4:3')).toBe(75);
    expect(calcAspectRatioHeight(100, '5:4')).toBe(80);
    expect(calcAspectRatioHeight(100, '9:16')).toBe(177.77777777777777);
    expect(calcAspectRatioHeight(100, '16:9')).toBe(56.25);
    expect(calcAspectRatioHeight(100, '1:1')).toBe(100);
  });

  test('Should output correct height if width is passed as a string.', () => {
    expect(calcAspectRatioHeight('100', '16:9')).toBe(56.25);
  });

  test('Should output the default 16:9 height if the aspect ratio is invalid.', () => {
    expect(calcAspectRatioHeight(100, ':')).toBe(56.25);
    expect(calcAspectRatioHeight(100, '')).toBe(56.25);
    expect(calcAspectRatioHeight(100, 3495807)).toBe(56.25);
    expect(calcAspectRatioHeight(100, '//&:ll')).toBe(56.25);
    expect(calcAspectRatioHeight(1, '//&:luu')).toBe(0.5625);
    expect(calcAspectRatioHeight(78, ':')).toBe(43.875);
    expect(calcAspectRatioHeight(78, '')).toBe(43.875);
  });
});