JavaScript Object-oriented

There are three types of objects: built-in objects , DOM objects , custom Objects

what type of function is that, first look at this piece of code

function fn () {
Alert (' Hello World ');
}

FN ();

first declare , in the call , run successfully

var fn = function () {
Alert (' Hello World ');
};
FN ();

first declare , in the call , run successfully

FN ();
function fn () {
Alert (' Hello World ');
}

look at this code again , according to JS is the rule from the top down , the function called before the declaration is not possible , This code, however, also succeeded in ejecting the Hello world after it was run .

FN ();
var fn = function () {
Alert (' Hello World ');
};

An error indicating that FN is not a function

Reason is

function fn () {} is called the Declaration of functions , and var fn = function () {} is called the expression of the functions . the expression of a function must first be declared and then called , but the declaration of a function is special in that it can be called before declaring , JS the engine is parsing JS the code will first detect how many such functions , and declare it in advance .

function is not an object ? we are typeof a moment to find out function, that function not an object? ? there's a standard notation for functions. :

var fn = function () {

Alert (Hello World);

}

written as var fn = new Function ("Alert (Hello World);")

At this time, although the typeof is function , but in js , all new can be counted as objects . at this , function can count as an object.

Object Direct Volume :

in js , We can write the following code

var o = new Object ();

O.name = ' Lisi ';

O.sayhello = function () {

alert (hello);

}

In fact, there is a more intuitive way of writing, called the direct amount of the object

var o = {

Name: ' Lisi ',

Sayhello:function () {}

}

O.sayhello ();

This approach is simpler and more intuitive , and is equivalent to encapsulating some attribute methods in an object , and in the next programming I will only care about this object .

class : A collection of objects with the same methods and properties

Example : function Cat (name,age) {

THIS.name = name,

This.age = Age

}

Cat.prototype.eat = function () {

Console (AAA);

}

var cat1 = New Cat (' Mimi ', 3);

Cat1.eat ();

encapsulates a property into a class , encapsulating the method in the prototype prototype

You can use the class keyword directly in the es6

JavaScript Object-oriented