utility ("sugar") properties and functions inspired by Dart and C#

string.js

if (String.prototype.isEmpty == undefined) {
  Object.defineProperty(String.prototype, 'isEmpty', {
    get: function() { return this.trim() == ''; }
  });
}

if (String.prototype.isNotEmpty == undefined) {
  Object.defineProperty(String.prototype, 'isNotEmpty', {
    get: function() { return this.trim() != ''; }
  });
}

if (String.isNullOrEmpty == undefined) {
  Object.defineProperty(String, 'isNullOrEmpty', {
    value: (aString) => aString == null || (typeof aString === 'string' && aString.isEmpty),
    writable: false
  });
}

stringUtil.js

var StringUtil = Object.create({}, {
  isString:       { value: function(aString) { return typeof aString === 'string'; }},
  isEmpty:        { value: function(aString) { return this.isString(aString) && aString.trim() == ''; }},
  isNotEmpty:     { value: function(aString) { return !this.isEmpty(aString); }},
  isNullOrEmpty:  { value: function(aString) { return aString == null || this.isEmpty(aString); }},
  valueOrDefault: { value: function(aString, aDefault) { return this.isNullOrEmpty(aString) ? aDefault : aString; }}
});