Develop Reference

Javascript function does not return the right value

So i have this code:
function Class1() {
this.i = 1;
var that=this;
function nn() {
return 21;
}
this.aa = function() {
nn();
};
this.bb = function() {
this.aa();
};
this.cc = function() {
this.bb();
};
}
var o = new Class1();
var b=o.cc();
alert(b); //undefined
But when the alert is fired, I get an undefined error and not 21, Does the private method can not use a return? Thanks!

When using the function() {} syntax to define a function, you always explicitly need to return the value, i.e. not only from nn, but from all intermediate functions as well.
function Class1() {
this.i = 1;
var that = this;
function nn() {
return 21;
}
this.aa = function() {
return nn();
}
this.bb = function() {
return this.aa();
}
this.cc = function() {
return this.bb();
}
}
var o = new Class1();
var b = o.cc();
alert(b); // "21"

Apart from the answer above, the 'this' context seems weird in your functions. Maybe you are better of with arrow functions if you dont want to bind the this context to each function. I also think that it is better to actually separate private and public functions when using a 'class' like this.
function Class1() {
var _nn = function () {
return 21;
}
var _aa = function () {
return _nn();
}
var _bb = function () {
return _aa();
}
var cc = function () {
return _bb();
};
return {
cc
};
}
var o = new Class1();
var a = o.cc();
console.log(a);
Much easier to understand that it is only cc that is a public function.

So with arrow function it would instead look like this, and you can use the Class1 this context inside of your private functions without doing
var that = this; or using bind.
function Class1() {
this.privateThing = 'private';
var _nn = () => { return this.privateThing; };
var _aa = () => { return _nn(); };
var _bb = () => { return _aa(); };
var cc = () => { return _bb(); };
return {
cc
};
}

Can't have access to a variable using call in Javascript

I'm studying Javascript and learning how to use call. I created this script and I don't know why I can't have access to this variable Time.
var MyObject;
(function(MyObject) {
var Runner = (function() {
function Runner(time) {
this.time = time;
}
var myFunctionArray = [];
Runner.prototype.execute = function() {
myFunctionArray[0]();
}
Runner.prototype.newTest = function(index, execute) {
var test = function() {
return execute.call(this);
}
myFunctionArray.push(test);
}
return Runner;
})();
MyObject.Runner = Runner;
})(MyObject || (MyObject = {});
var myNewObj = new MyObject.Runner(1000); myNewObj.newTest('1', function() {
console.log(this.time) //output: undefined
});
So how can I get time value inside newTest function?

Issue is in newTest function
Runner.prototype.newTest = function(index, execute) {
var test = function() {
return execute.call(this);
}
myFunctionArray.push(test);
}
Here this is pointing to test and not Runner. You will have to save context in a variable and then set it in call.
Runner.prototype.newTest = function(index, execute) {
var self = this;
var test = function() {
return execute.call(self);
}
myFunctionArray.push(test);
}
.call + self
var MyObject;
(function(MyObject) {
var Runner = (function() {
function Runner(time) {
this.time = time;
}
var myFunctionArray = [];
Runner.prototype.execute = function() {
myFunctionArray[0]();
}
Runner.prototype.newTest = function(index, execute) {
var self = this;
var test = function() {
return execute.call(self);
}
myFunctionArray.push(test);
}
return Runner;
})();
MyObject.Runner = Runner;
})(MyObject || (MyObject = {}));
var myNewObj = new MyObject.Runner(1000);
myNewObj.newTest('1', function() {
console.log(this, this.time) //output: undefined
});
myNewObj.execute()
.bind
As commented, you can even use .bind
var MyObject;
(function(MyObject) {
var Runner = (function() {
function Runner(time) {
this.time = time;
}
var myFunctionArray = [];
Runner.prototype.execute = function() {
myFunctionArray[0]();
}
Runner.prototype.newTest = function(index, execute) {
myFunctionArray.push(execute.bind(this));
}
return Runner;
})();
MyObject.Runner = Runner;
})(MyObject || (MyObject = {}));
var myNewObj = new MyObject.Runner(1000);
myNewObj.newTest('1', function() {
console.log(this, this.time) //output: undefined
});
myNewObj.execute()

When you declare your Runner function, you've actually declared a function that takes no arguments that then itself declares a function called Runner that takes one argument.

Actually In this code snippet :
Runner.prototype.newTest = function(index, execute) {
var test = function() {
return execute.call(this);
}
myFunctionArray.push(test);
}
this will reference to test variable (as per constructor invocation pattern)
So, to pass right variable cache the value of this in another variable and then pass that to function.

what is wrong with this piece of code of javascript inheritance?

function condition(){
this.expression = "";
this.toString = function(){
return this.expression;
}
};
function and(first, second){
this.expression = first + " and " + second;
}
function nop(){};
nop.prototype = condition.prototype;
and.prototype = new nop();
var a =new and(1,2);
console.log(a.toString());
it is expected to see "1 and 2" as output but this is what happened:
"[object Object]"

You are transfering the prototype of condition to nop's prototype. The problem is that your condition.toString is not declared in the prototype... Here:
function condition(){
this.expression = "";
};
condition.prototype.toString = function(){
return this.expression;
}
function and(first, second){
this.expression = first + " and " + second;
}
function nop(){};
nop.prototype = condition.prototype;
and.prototype = new nop();
var a =new and(1,2);
console.log(a.toString());
OR
function condition(){
this.expression = "";
this.toString = function(){
return this.expression;
}
};
function and(first, second){
this.expression = first + " and " + second;
}
function nop(){};
nop = condition;
and.prototype = new nop();
var a =new and(1,2);
console.log(a.toString());

you aren't overriding the toString method, because the constructer of condition is never called! try doing this;
condition.prototype.toString=function(){
return this.expression;
}

try passing strings into your and function, as at the moment you are trying to concatenate integers to a string var a =new and("1","2");

it should be like this
function condition(){
this.expression = "";
};
condition.prototype.toString = function(){
return this.expression;
}

Ok, so the problem here is you are mixing two inheritance patterns (http://davidshariff.com/blog/javascript-inheritance-patterns/) the pseudo-classical with the functional patterns.
You can create an object by adding methods on the constructor function:
function MyClass() {
var privateProperty = 1;
this.publicProperty = 2;
function pivateMethod() {
// some code ...
}
this.publicMethod = function() {
// some code ...
};
}
// inheritance
function SubClass() {
MyClass.call(this);
this.newMethod = function() { };
}
Here when you create a instance of this class you are creating every method again.
Then you have the prototype pattern:
function MyClass() {
this._protectedProperty = 1;
this.publicProperty = 2;
}
MyClass.prototype._protectedMethod = function() {
// some code ...
};
MyClass.prototype.publicMethod = function() {
// some code ...
};
// inheritance
function SubClass() {
MyClass.call(this);
}
SubClass.prototype = new MyClass();
SubClass.prototype.newMethod = function() { };
// OR
function SubClass() {
MyClass.call(this);
}
function dummy() { }
dummy.prototype = MyClass.prototype;
SubClass.prototype = new dummy();
SubClass.prototype.newMethod = function() { };
Yhen you must choose one of those two patterns, not both·
I've fixed your code on this fiddle: http://jsfiddle.net/dz6Ch/

How do I do JavaScript Prototype Inheritance (chain of prototypes)

This is a question for the guru of JavaScript. I'm trying to do work with JavaScript prototype model more elegant. Here is my utility code (it provides real chain of prototypes and correct work with instanceof operator):
function Class(conf) {
var init = conf.init || function () {};
delete conf.init;
var parent = conf.parent || function () {};
delete conf.parent;
var F = function () {};
F.prototype = parent.prototype;
var f = new F();
for (var fn in conf) f[fn] = conf[fn];
init.prototype = f;
return init;
};
It allows me to do such thigns:
var Class_1 = new Class({
init: function (msg) { // constructor
this.msg = msg;
},
method_1: function () {
alert(this.msg + ' in Class_1::method_1');
},
method_2: function () {
alert(this.msg + ' in Class_1::method_2');
}
});
var Class_2 = new Class({
parent: Class_1,
init: function (msg) { // constructor
this.msg = msg;
},
// method_1 will be taken from Class_1
method_2: function () { // this method will overwrite the original one
alert(this.msg + ' in Class_2::method_2');
},
method_3: function () { // just new method
alert(this.msg + ' in Class_2::method_3');
}
});
var c1 = new Class_1('msg');
c1.method_1(); // msg in Class_1::method_1
c1.method_2(); // msg in Class_1::method_2
var c2 = new Class_2('msg');
c2.method_1(); // msg in Class_1::method_1
c2.method_2(); // msg in Class_2::method_2
c2.method_3(); // msg in Class_2::method_3
alert('c1 < Class_1 - ' + (c1 instanceof Class_1 ? 'true' : 'false')); // true
alert('c1 < Class_2 - ' + (c1 instanceof Class_2 ? 'true' : 'false')); // false
alert('c2 < Class_1 - ' + (c2 instanceof Class_1 ? 'true' : 'false')); // true
alert('c2 < Class_2 - ' + (c2 instanceof Class_2 ? 'true' : 'false')); // true
My question is: Is there more simple way to do this?

Yes, there is a better way to do this.
var call = Function.prototype.call;
var classes = createStorage(),
namespaces = createStorage(),
instances = createStorage(createStorage);
function createStorage(creator){
var storage = new WeakMap;
creator = typeof creator === 'function' ? creator : Object.create.bind(null, null, {});
return function store(o, v){
if (v) {
storage.set(o, v);
} else {
v = storage.get(o);
if (!v) {
storage.set(o, v = creator(o));
}
}
return v;
};
}
function Type(){
var self = function(){}
self.__proto__ = Type.prototype;
return self;
}
Type.prototype = Object.create(Function, {
constructor: { value: Type,
writable: true,
configurable: true },
subclass: { value: function subclass(scope){ return new Class(this, scope) },
configurable: true,
writable: true }
});
function Class(Super, scope){
if (!scope) {
scope = Super;
Super = new Type;
}
if (typeof Super !== 'function') {
throw new TypeError('Superconstructor must be a function');
} else if (typeof scope !== 'function') {
throw new TypeError('A scope function was not provided');
}
this.super = Super;
this.scope = scope;
return this.instantiate();
}
Class.unwrap = function unwrap(Ctor){
return classes(Ctor);
};
Class.prototype.instantiate = function instantiate(){
function super_(){
var name = super_.caller === Ctor ? 'constructor' : super_.caller.name;
var method = Super.prototype[name];
if (typeof method !== 'function') {
throw new Error('Attempted to call non-existent supermethod');
}
return call.apply(method, arguments);
}
var Super = this.super,
namespace = namespaces(Super),
private = instances(namespace)
var Ctor = this.scope.call(namespace, private, super_);
Ctor.__proto__ = Super;
Ctor.prototype.__proto__ = Super.prototype;
namespaces(Ctor, namespace);
classes(Ctor, this);
return Ctor;
}
example usage:
var Primary = new Class(function(_, super_){
var namespace = this;
namespace.instances = 0;
function Primary(name, secret){
this.name = name;
_(this).secret = secret;
namespace.instances++;
}
Primary.prototype.logSecret = function logSecret(label){
label = label || 'secret';
console.log(label + ': ' + _(this).secret);
}
return Primary;
});
var Derived = Primary.subclass(function(_, super_){
function Derived(name, secret, size){
super_(this, name, secret);
this.size = size;
}
Derived.prototype.logSecret = function logSecret(){
super_(this, 'derived secret');
}
Derived.prototype.exposeSecret = function exposeSecret(){
return _(this).secret;
}
return Derived;
});
var Bob = new Derived('Bob', 'is dumb', 20);
Bob.logSecret();
console.log(Bob);
console.log(Bob.exposeSecret());

After some research I've concluded there is no more simple way to do this.

Javascript Metaprogramming

Is there a way to specify something similar to the following in javascript?
var c = {};
c.a = function() { }
c.__call__ = function (function_name, args) {
c[function_name] = function () { }; //it doesn't have to capture c... we can also have the obj passed in
return c[function_name](args);
}
c.a(); //calls c.a() directly
c.b(); //goes into c.__call__ because c.b() doesn't exist

Mozilla implements noSuchMethod but otherwise...no.

No, not really. There are some alternatives - though not as nice or convenient as your example.
For example:
function MethodManager(object) {
var methods = {};
this.defineMethod = function (methodName, func) {
methods[methodName] = func;
};
this.call = function (methodName, args, thisp) {
var method = methods[methodName] = methods[methodName] || function () {};
return methods[methodName].apply(thisp || object, args);
};
}
var obj = new MethodManager({});
obj.defineMethod('hello', function (name) { console.log("hello " + name); });
obj.call('hello', ['world']);
// "hello world"
obj.call('dne');

Almost 6 years later and there's finally a way, using Proxy:
const c = new Proxy({}, {
get (target, key) {
if (key in target) return target[key];
return function () {
console.log(`invoked ${key}() from proxy`);
};
}
});
c.a = function () {
console.log('invoked a()');
};
c.a();
c.b();

No.