“new” operator before declaring function

Question

Like explore javascript as my first reference to the whole programming but as i\'m not the professional can\'t comprehend a lot of stuff. So it would be so much appreciated if

Answer 1

Those are completely different things. The second one is a standard javascript function declaration (and can be called with sayHi();), while the first should be rewritten as

new (function sayHi() { alert('hi'); });

Now you can see it is a (named) function expression, which is directly passed to the new operator. This should not be used, if you really wanted to call it immediately (there are applications) use (function(){…})());.

Answer 2

1) you don't use new when defining the function, but rather you use new when you call the function with the intent to make a new object.

2) if you use new when you're defining the function, it means that it will fire right away. This can be handy sometimes... ...but it's really not how a beginner should learn. Also, the more-accepted version of this technique is called an IIFE (Immediately Invoked Function Expression), which looks like

(function () {
/* function stuff in here */
}());

instead of

new function () { /* function stuff in here */ }

If you try to define a function that way, you will get an error if you try to use it, later (because it's not defined).

Here are two ways of actually defining functions:

var sayHi = function () { console.log("Hi!"); };

and

function sayHello () { console.log("Hello"); }

Neither of these use new.

In order to call them, and have them do their job, you don't need to use .call(). .call() will work, but it has a special purpose which you won't need for a very long time.

All you need to do is this:

sayHello();
sayHi();

New is intended to be used when you want to make a certain kind of object.

Making objects in JavaScript is very simple:

var obj = {};
var person = { name : "Bob" };

person.name; // "Bob"
person.age = 32;

Working with objects is very, very easy.

But in other programming languages, you need classes which are like blueprints for an object.

In JS, you might make a class like this:

function Person (name, age) { this.name = name; this.age = age; }

and then use it like:

var bob = new Person("Bob", 32);
bob.name; // "Bob";
bob.age;  // 32;

See where I put the new?
I used a function which makes people, and I said that I want bob to be a new Person.

But again, in JS, this can be as easy as:

var mike = { name : "Mike", age : 20 };

Didn't have to build a function, didn't have to use new. It just worked.