"Learning Essays" JS initial involvement

JS = JavaScript

He's a lightweight, other programming language.

Page code that can be inserted into HTML

After inserting an HTML page, it can be performed by all browsers now

Output statement: Document.writie ();

Declaring variables: Var eg:var A;

Assignment: = eg:a = 1;

JS data type: String numeric Boolean array object null undefined

String: var x = "Bill";

Number: var x = 5;

Boolean value: var x = true;

Array: var x = new Array ();

X[0] = "Music";

X[1] = "BMW";

X[2] = "Hello";

Or: Var cars=new Array ("Audi", "BMW", "Volvo");

var cars=["Audi", "BMW", "Volvo";

Object: var person={firstname: "Bill", LastName: "Gates", id:5566};

var person={

FirstName: "Bill,"

LastName: "Gates",

id:5566

};

Object properties are addressed in two ways, for example: Name=person.lastname;

name=person["LastName"];

Eg: <script>

var person={

FirstName: "Bill,"

LastName: "Gates",

id:5566

};

document.write (person.lastname + "<br/>");

document.write (person["LastName"] + "<br/>");

</script>

Undefined This value indicates that the variable does not contain a value.

Null indicates that the variable value is set to NULL

When declaring a new variable, you can use the keyword "new" to declare its type, for example:

var carname=new String;

var x= new number;

var y= new Boolean;

var cars= new Array;

var person= new Object;

JS Object

All things in JavaScript are objects: strings, numbers, arrays, dates, and so on. In JavaScript, objects are data that owns properties and methods.

Properties and Methods

A property is a value associated with an object.

Method is an action that can be performed on an object.

Create objects, such as:

Person=new Object ();

Person.firstname= "Bill";

Person.lastname= "Gates";

person.age=56;

Person.eyecolor= "Blue";

Here the person is the object, FirstName, LastName, age, Eyecolor are attributes, the right side of the equals sign is the value of the property

How do I access an object?

Syntax: Objectname.methodname ()

Function:

A function is an event-driven or reusable block of code that executes when it is invoked. Key words: function

Syntax: function functionname ()

{

Here is the code to execute

}

Note that function must be lowercase, and if onclick= "method name", then two of the function method name () must correspond.

Calling a function with parameters

When you call a function, you can pass a value to it, which is called a parameter. These parameters can be used in functions. You can also send any number of arguments, separated by commas (,): MyFunction (Argument1,argument2)

When declaring a function, declare the argument as a variable:

function MyFunction (var1,var2) {}

Variables and parameters must appear in a consistent order. The first variable is the given value of the first parameter passed, and so on. For example:

<button onclick= "myFunction (' Bil ')" > click here </button>

<script>

function MyFunction (name)

{

alert (name);

}

</script>

JavaScript provides multiple built-in objects, such as String, Date, Array, and so on.

To access the object's properties, syntax:

Objectname.propertyname

Methods for accessing objects

Methods are actions that can be performed on an object, and methods are invoked through the following syntax:

Objectname.methodname ()

There are two different ways to create a new object:

1 defining and creating an instance of an object

Person=new Object ();

Person.firstname= "Bill";

Person.lastname= "Gates";

person.age=56;

Person.eyecolor= "Blue";

2 Use a function to define an object, and then create a new object instance

function person (firstname,lastname,age,eyecolor)

{

This.firstname=firstname;

This.lastname=lastname;

This.age=age;

This.eyecolor=eyecolor;

}

"Learning Essays" JS initial involvement