mathjs/src/utils/polyfills.js

// TODO: remove these polyfills as soon as we have a build process that transpiles the code to ES5

// Polyfill for IE 11 (Number.isFinite is used in `complex.js`)
// source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isFinite
Number.isFinite = Number.isFinite || function (value) {
  return typeof value === 'number' && isFinite(value)
}

// Polyfill for IE 11
// source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN
Number.isNaN = Number.isNaN || function (value) {
  return value !== value // eslint-disable-line no-self-compare
}