Assert that good for debugging

assert.js

function Test(a, b){ // noprotect
   assert(typeOf({a:a}, 'string'), function(m){ throw m });
   assert(typeOf({b:b}, 'string'), function(m){ throw m });
  
   var result = a + b;
   result = null;
  
   assert(notNullOrUndefined({result:result}), function(m){ throw m });
   assert(equal({result:result}, 'ac'), function(m){ throw m });
   return result;
}

function assert(isValid, errorCallback) { 
  var check = isValid();
  
  if (check.message) {
    if (!check.isValid) {
      errorCallback(check.message);
    }
  } else {
    errorCallback();
  }
}

function typeOf(val, type) {
  return function (){
    var firstProp = getFirstPropName(val);
    var firstVal = val[firstProp];
    return {
      isValid: typeof firstVal === type,
      message: '[' + firstProp + '] must be a type of "' + type + '", current type is "' + (typeof firstVal) + '"'
    };
  };
}

function equal(val, valToComare) {
  return function(){
    var firstProp = getFirstPropName(val);
    var firstVal = val[firstProp];
    return {
      isValid: firstVal === valToComare,
      message: '[' + firstProp + '] must be equal to "' + valToComare + '", current value is "' + firstVal  + '"'
    };
  };
};

function notNullOrUndefined(val) {
  return function(){
    var firstProp = getFirstPropName(val);
    var firstVal = val[firstProp];
    return {
      isValid: firstVal != null,
      message: '[' + firstProp + '] must not be Null or Undefined, current value is "' + firstVal  + '"'
    };
  };
}

function getFirstPropName(obj){
  for (var key in obj){
    if (obj.hasOwnProperty(key)) {
      return key;
    }
  }
  return null;
}

console.log(Test('a', 'b'));

c-assert.coffee

Test = (a, b) -> # noprotect
  assert typeOf(a:a, "string"), (m) -> throw m
  assert typeOf(b:b, "string"), (m) -> throw m

  result = a + b
  result = null

  assert notNullOrUndefined(result:result), (m) -> throw m
  assert equal(result:result), (m) -> throw m
  result

assert = (isValid, errorCallback) ->
  check = isValid()
  if check.message
    errorCallback check.message  unless check.isValid
  else
    errorCallback()
  return

typeOf = (val, type) ->
  ->
    firstProp = getFirstPropName(val)
    firstVal = val[firstProp]
    isValid: typeof firstVal is type
    message: "[" + firstProp + "] must be a type of \"" + type + "\", current type is \"" + (typeof firstVal) + "\""

equal = (val, valToComare) ->
  ->
    firstProp = getFirstPropName(val)
    firstVal = val[firstProp]
    isValid: firstVal == valToComare
    message: '[' + firstProp + '] must be equal to "' + valToComare + '", current value is "' + firstVal + '"'
    
notNullOrUndefined = (val) ->
  ->
    firstProp = getFirstPropName(val)
    firstVal = val[firstProp]
    isValid: firstVal?
    message: "[" + firstProp + "] must not be Null or Undefined, current value is \"" + firstVal + "\""

getFirstPropName = (obj) ->
  for key of obj
    return key  if obj.hasOwnProperty(key)
  null

console.log Test("a", "b")