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javascript数据类型 -JavaScript优势简介及数据类型

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JavaScript优势简介及数据类型 Introduction to JavaScript, Advantages, Data Types – Variables – Operators - Control Statements – Functions - Objects – Array – Strings – Math – Boolean – Global - Date, and Number - Windows and Frames - Forms and Validation. JavaScript简介 Javascript是一种动态计算机编程语言。它是轻量级的，最常用作网页的一部分，其实现允许客户端脚本与用户交互并生成动态页面。它是一种具有面向对象功能的解释性编程语言。

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javascript数据类型

COURSE CODE : SIT1302

COURSE NAME: INTERNET PROGRAMMING

CHAPTER NAME : JAVA SCRIPT

Introduction to JavaScript, Advantages, Data Types – Variables – Operators - Control

Statements – Functions - Objects – Array – Strings – Math – Boolean – Global - Date, and

Number - Windows and Frames - Forms and Validation.

Introduction to JavaScript

Javascript is a dynamic computer programming language. It is lightweight and most commonly

used as a part of web pages, whose implementations allow client-side script to interact with the

user and make dynamic pages. It is an interpreted programming language with object-oriented

capabilities.

Advantages

 Less server interaction − You can validate user input before sending the page off to the

server. This saves server traffic, which means less load on your server.

 Immediate feedback to the visitors − They don't have to wait for a page reload to see if

they have forgotten to enter something.

 Increased interactivity − You can create interfaces that react when the user hovers over

them with a mouse or activates them via the keyboard.

 Richer interfaces − You can use JavaScript to include such items as drag-and-drop

components and sliders to give a Rich Interface to your site visitors.

Data Types

JavaScript allows you to work with three primitive data types

 Numbers, eg. 123, 120.50 etc.

 Strings of text e.g. "This text string" etc.

 Boolean e.g. true or false.

Trivial data types

null and undefined, each of which defines only a single value.

composite data type

object

Variables

Variables are declared with the var keyword as follows. JavaScript is untyped language. This

means that a JavaScript variable can hold a value of any data type.

<!--

var money;

var name;

//-->

</script>

You can also declare multiple variables with the same var keyword as follows −

<!--

var money, name;

//-->

</script>

Storing a value in a variable is called variable initialization.

<!--

var name = "Ali";

var money;

money = 2000.50;

//-->

</script>

JavaScript Variable Scope

The scope of a variable is the region of your program in which it is defined. JavaScript variables

have only two scopes.

 Global Variables − A global variable has global scope which means it can be defined

anywhere in your JavaScript code.

 Local Variables − A local variable will be visible only within a function where it is

defined. Function parameters are always local to that function.

Within the body of a function, a local variable takes precedence over a global variable with the

same name.

<html>

<!--

var myVar = "global"; // Declare a global variable

function checkscope( ) {

var myVar = "local"; // Declare a local variable

document.write(myVar);

}

//-->

</script>

</body>

</html>

This produces the following result −

local

Operators

What is an operator?

Let us take a simple expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and ‘+’ is

called the operator. JavaScript supports the following types of operators.

 Arithmetic Operators

 Comparison Operators

 Logical (or Relational) Operators

 Assignment Operators

 Conditional (or ternary) Operators

Arithmetic Operators

+ , - , / , *, %, ++, --

The following code shows how to use arithmetic operators in JavaScript.

<html>

<body>

<!--

var a = 33;

var b = 10;

var c = "Test";

var linebreak = "<br />";

document.write("a + b = ");

result = a + b;

document.write(result);

document.write(linebreak);

document.write("a - b = ");

result = a - b;

document.write(result);

document.write(linebreak);

document.write("a / b = ");

result = a / b;

document.write(result);

document.write(linebreak);

document.write("a % b = ");

result = a % b;

document.write(result);

document.write(linebreak);

document.write("a + b + c = ");

result = a + b + c;

document.write(result);

document.write(linebreak);

a = ++a;

document.write("++a = ");

result = ++a;

document.write(result);

document.write(linebreak);

b = --b;

document.write("--b = ");

result = --b;

document.write(result);

document.write(linebreak);

//-->

</script>

Set the variables to different values and then try...

</body>

</html>

Output

a + b = 43

a - b = 23

a / b = 3.3

a % b = 3

a + b + c = 43Test

++a = 35

--b = 8

Set the variables to different values and then try...

Comparison Operators

==,!=.>,>=,<,<=

The following code shows how to use comparison operators in JavaScript.

<html>

<body>

<!--

var a = 10;

var b = 20;

var linebreak = "<br />";

document.write("(a == b) => ");

result = (a == b);

document.write(result);

document.write(linebreak);

document.write("(a < b) => ");

result = (a < b);

document.write(result);

document.write(linebreak);

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