An extended version of the typeOf() function which will either return the name of the class, "null", "undefined" or a boolean indicating if one of the passed type names matches the type of the value.

typeOf.js

function typeOf(value) {
  for (
    var test,
        argv = arguments,
        argc = argv.length,
        i = argc,
        typeName = value == undefined
          ? value === undefined
            ? 'undefined'
            : 'null'
          : {}.toString.call(value).slice(8, -1);
    --i > 0 && ((typeof(test = argv[i]) == 'string' || typeOf(test) != 'RegExp') ? typeName != test : !test.test(typeName));
  );
  return argc > 1 ? !!i : typeName;
}

Console tests where only the value is supplied:

console.log(typeOf());           // "undefined"
console.log(typeOf(3));          // "Number"
console.log(typeOf([6]));        // "Array"
console.log(typeOf(null));       // "null"
console.log(typeOf(false));      // "Boolean"
console.log(typeOf(typeOf));     // "Function"
console.log(typeOf("Cool!"));    // "String"
console.log(typeOf(new Date));   // "Date"
console.log(typeOf(undefined));  // "undefined"
console.log(typeOf(/^ +| +$/i)); // "RegExp"

Console tests where the value is tested against strings and regular expressions:

console.log(typeOf(3, "Number"));                         // true
console.log(typeOf(4, "String"));                         // false
console.log(typeOf(5, "String", "Number"));               // true
console.log(typeOf("6", /Number|String/));                // true
console.log(typeOf(null, /^[nu]/));                       // true
console.log(typeOf(undefined, /^[A-Z]/, 'undefined'));    // true
console.log(typeOf([6], "Array"));                        // true
console.log(typeOf(false, "Function", "Date"));           // false
console.log(typeOf(true, "Function", "Date", "Boolean")); // true