function isNumber(value) {
      return typeof value == 'number' ||
        value && typeof value == 'object' && toString.call(value) == numberClass || false;
    }
Checks if `value` is a number.

Note: `NaN` is considered a number. See http://es5.github.io/#x8.5.

@static
@memberOf _
@category Objects
@param {*} value The value to check.
@returns {boolean} Returns `true` if the `value` is a number, else `false`.
@example

_.isNumber(8.4 * 5);
// => true