mathjs/lib/util/types.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser and offers an integrated solution to work with numbers, big numbers, complex numbers, units, and matrices.

/**
 * Determine the type of a variable
 *
 *     typeof(x)
 *
 * @param {*} x
 * @return {String} type  Lower case type, for example 'number', 'string',
 *                        'array', 'date'.
 */
exports.type = function type (x) {
  var type = typeof x;

  if (type === 'object') {
    if (x === null) {
      return 'null';
    }
    if (x instanceof Boolean) {
      return 'boolean';
    }
    if (x instanceof Number) {
      return 'number';
    }
    if (x instanceof String) {
      return 'string';
    }
    if (Array.isArray(x)) {
      return 'array';
    }
    if (x instanceof Date) {
      return 'date';
    }
  }

  return type;
};