Sometimes I want to split an integer.

split.js

(({ defineProperty }, { prototype }) => (
  defineProperty(prototype, 'divmod', {
    value(a) {
      return (
        a === 0 ? [0, this.valueOf()] :
        ((r) => (
          ((q) => (
            [q, r]
          ))((this - r) / a)
        ))(this % a)
      )
    }
  }),
  defineProperty(prototype, 'split', {
    value(a) {
      return (
        this < a ? [ this.valueOf() ] :
        (([q, r]) => (
          q.split(a).concat(r)
        ))(this.divmod(a))
      )
    }
  })
))(Reflect, Number)

Reflect.defineProperty(String.prototype, 'inv', { get() { return this.split('').reverse().join('') } })
String(2**52).inv.match(/(.{1,4})/g).map(a => a.inv).reverse()