How to call function from object

Question

I try to call function from object Foo but it doesn't work.

function Foo(){
 function bar(){
 alert("Hello!");
 } 
}
var a = new Foo();
a.bar();

• jfriend00: As you have declared it bar() is a local function that is only available inside of the Foo() function.
• Jai: Such a basic question should not be asked as you can find so many tutorials on Internet.

Answer 1

you should set the function as object's property

function Foo(){
 this.bar = function (){
 alert("Hello!");
 };
}
var a = new Foo();
a.bar();

or use prototype to define it before object creation

function Foo(){}
Foo.prototype.bar = function (){
 alert("Hello!");
};
var a = new Foo();
a.bar();

Answer 2

In addition to @user3896501's answer,

function Foo() {
 // You can define all private variables/ functions.
 function bar(callBar1) {
 alert("Hello!");
 if (callBar1)
 bar1();
 }
 // This is a private function and can be called only from inside.
 function bar1() {
 alert("Hello!!!");
 }
 // Return only those variables/ functions which needs to be made public
 return {
 bar: bar
 }
}
var a = new Foo();
a.bar();
// Trying to access private function should throw exception
try {
 a.bar1();
} catch (e) {
 console.log(e)
}
// Accessing private function using parameter
a.bar(true);

Answer 3

function Foo()
{
 // ...
}
Foo.prototype.bar = function ()
{
 alert("I called bar on a Foo object");
};
var a = new Foo();
a.bar();

Answer 4

 function Foo(){
 function bar(){
 alert("Hello!");
 } 
 return {
 bar : bar
 }
}
var a = new Foo();
a.bar();