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📜  var js - Javascript (1)

📅  最后修改于: 2023-12-03 14:48:16.463000             🧑  作者: Mango

Introduction to Javascript

Javascript is a programming language that is commonly used to create interactive web pages, web applications, and server-side applications. It is a scripting language, which means that it is interpreted by a browser or a server, rather than being compiled like other programming languages.

Basic Syntax

Javascript code can be embedded in HTML web pages using the <script> tag. Here is an example:

<!DOCTYPE html>
<html>
<head>
	<title>My Javascript Page</title>
</head>
<body>
	<script>
		var message = "Hello World!";
		alert(message);
	</script>
</body>
</html>

In this example, the var keyword is used to declare a variable called message, which is set to the string "Hello World!". The alert() function is then used to display the contents of the message variable in a pop-up window.

Data Types

Javascript supports several data types, including:

  • Number: represents numeric values, such as 42 or 3.14.
  • String: represents textual data, such as "Hello" or "World".
  • Boolean: represents the values true or false.
  • Undefined: represents a variable that has not been assigned a value.
  • Null: represents a variable that has been explicitly set to null.
  • Object: represents complex data structures.
Control Structures

Javascript provides several control structures that allow programmers to control the flow of their code. These include:

  • if/else statements: allow code to be executed conditionally based on the result of a logical expression.
  • while loops: allow code to be executed repeatedly while a condition is true.
  • for loops: allow code to be executed repeatedly for a specific number of times.
  • switch statements: allow code to be executed conditionally based on the value of a variable.
Functions

Functions are a fundamental building block of Javascript. They allow programmers to define reusable blocks of code that can be called from different parts of their program. Here is an example of a simple function:

function greet(name) {
	alert("Hello, " + name + "!");
}

greet("World");

In this example, the greet() function takes a parameter called name, which is used to construct a greeting message. The function is then called with the argument "World", which results in the message "Hello, World!" being displayed in a pop-up window.

Conclusion

Javascript is a powerful language that is widely used in web development. It provides developers with a wide range of functionality, from basic data types to complex control structures and functions. With its ubiquity and versatility, Javascript is a valuable tool for any programmer to have in their toolbox.