really simple javascript type detection

whatis.js

const assert = function (condition) {
  if (condition !== true && condition !== false) {
    throw new TypeError("Assertions should be only of booleans; you're writing your spec wrong.");
  }

  if (!condition) {
    throw new Error("Specification-level assertion failure");
  }
};
function whatIs(this$) {
  switch(typeof this$) {
  case 'string':
    return 'string'
  case 'object':
    if (this$ === null) return 'null'
    if (Array.isArray(this$)) return 'array'
    return 'object'
  case 'number':
    if (Number.isNaN(this$)) return 'nan'
    if (Number.isSafeInteger(this$)) return 'number'
    if (Number.isFinite(this$)) return 'float'
    return 'infinity'
  case 'undefined':
    return 'undefined'
  case 'function':
    return 'function'
  case 'boolean':
    return 'boolean'
  case 'symbol':
    return 'symbol'
  default:
    return 'unsure?'
  }
}
assert(whatIs(Math.PI) === 'float')
assert(whatIs(666) === 'number')
assert(whatIs(+0) === 'number')
assert(whatIs(-0) === 'number')
assert(whatIs('hello world') === 'string')
assert(whatIs(undefined) === 'undefined')
assert(whatIs(Infinity) === 'infinity')
assert(whatIs(-Infinity) === 'infinity')
assert(whatIs(+Infinity) === 'infinity')
assert(whatIs({}) === 'object')
assert(whatIs([]) === 'array')
assert(whatIs(function(){}) === 'function')
assert(whatIs(null) === 'null')
assert(whatIs(true) === 'boolean')
assert(whatIs(Symbol()) === 'symbol')
// assert(whatIs({"a":"a"}) === 'json') // soon... soon...