lodash/lang/isNumber.js

define(['../internal/isObjectLike'], function(isObjectLike) {

  /** `Object#toString` result references. */
  var numberTag = '[object Number]';

  /** Used for native method references. */
  var objectProto = Object.prototype;

  /**
   * Used to resolve the `toStringTag` of values.
   * See the [ES spec](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.tostring)
   * for more details.
   */
  var objToString = objectProto.toString;

  /**
   * Checks if `value` is classified as a `Number` primitive or object.
   *
   * **Note:** To exclude `Infinity`, `-Infinity`, and `NaN`, which are classified
   * as numbers, use the `_.isFinite` method.
   *
   * @static
   * @memberOf _
   * @category Lang
   * @param {*} value The value to check.
   * @returns {boolean} Returns `true` if `value` is correctly classified, else `false`.
   * @example
   *
   * _.isNumber(8.4);
   * // => true
   *
   * _.isNumber(NaN);
   * // => true
   *
   * _.isNumber('8.4');
   * // => false
   */
  function isNumber(value) {
    return typeof value == 'number' || (isObjectLike(value) && objToString.call(value) == numberTag) || false;
  }

  return isNumber;
});