Object.essence.js

/**
 * by Dmitry A. Soshnikov
 */

Object.defineProperty(Object, "essence", {
  value: function objectEssence(value) {
    var essence = {kind: Object.prototype.toString.call(value).slice(8, -1)};
    // use Object(value) just for shortness, it's less effective
    // than typeof value == "object" && value !== null || typeof value == "function"
    essence[value === Object(value) ? "object" : "primitive"] = true;
    return essence;
  }
});

var info = Object.essence;

// numbers
info(1);                  // {primitive: true, kind: "Number"}
info(new Number(1));      // {object:    true, kind: "Number"}

// null, undefined
info(null);               // {primitive: true, kind: "Null"}
info(undefined);          // {primitive: true, kind: "Undefined"}

// strings
info("1");                // {primitive: true, kind: "String"}
info(new String("1"));    // {object:    true, kind: "String"}

// regexp
info(/(?:)/);             // {object: true, kind: "RegExp"}

// array
info([]);                 // {object: true, kind: "Array"}

// object
info({});                 // {object: true, kind: "Object"}

(function () {
  info(arguments);        // {object: true, kind: "Arguments"}
})();

info(function () {});     // {object: true, kind: "Function"}

// etc.

Yeah, good catch. Then typeof is not needed at all in such test. Although method call for Object should be slower, then using typeof operator (in theory, however, I didn't check it in implementations).