getType

Returns the native type of a value.

• Return 'undefined' or 'null' if the value is undefined or null.
• Otherwise, use Object.prototype.constructor.name to get the name of the constructor.

const getType = v =>
  (v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name);

getType(new Set([1, 2, 3])); // 'Set'