A couple of useful utility functions for working with JS types.

TypeUtil.js

;(function() {


var global = this;


// Get the default value for a named type (primitive name, 'function' or name of constructor).
function defaultValue(type) {
    if (typeof type !== 'string') throw new TypeError('Type must be a string.');

    // Handle simple types (primitives and plain function/object)
    switch (type) {
        case 'boolean'   : return false;
        case 'function'  : return function () {};
        case 'null'      : return null;
        case 'number'    : return 0;
        case 'object'    : return {};
        case 'string'    : return "";
        case 'symbol'    : return Symbol();
        case 'undefined' : return void 0;
    }

    try {
        // Look for constructor in this or current scope
        var ctor = typeof this[type] === 'function'
                   ? this[type]
                   : eval(type);

        return new ctor;

    // Constructor not found, return new object
    } catch (e) { return {}; }
}


// Get the type name of an object (primitive name, 'function' or name of constructor).
function getType(obj) {
    var type = typeof obj;

    if (type !== 'object') return type; // primitive or function
    if (obj === null) return 'null';    // null

    // Everything else, check for a constructor
    var ctor = obj.constructor;
    var name = typeof ctor === 'function' && ctor.name;

    return typeof name === 'string' && name.length > 0 ? name : 'object';
}


var TypeUtil = {
    defaultValue : defaultValue,
    getType      : getType
};


if (typeof module !== 'undefined' && module.exports) {
    exports = module.exports = TypeUtil;

} else {
    global.TypeUtil = TypeUtil;
}


}).call(this);