Basic usage of Javascript

These are the most basic rules and methods of using Javascript that I have compiled. Through the study of these knowledge, you can have the most basic knowledge and understanding of Javascript.

1. How to use JS code:

Use the tag in the HTML web page, JavaScript code. Note that tags should appear in pairs, and write JavaScript code between .

means that the text type (text) between is used to tell the browser that the text in it belongs to JavaScript language.

2. Reference JS external files:

Tags add JavaScript code in HTML files. HTML files and JS codes can be separated. HTML files and JS codes can be separated, and Create a separate JavaScript file (JS file for short), the file suffix is usually .js, and then write the JS code directly in the JS file.

3. The position of JS in the page:

Place the JavaScript code anywhere in the html file. As a scripting language, javascript can be placed in the html page. Any position, but the browser interprets HTML in order, so the previous script is executed first. For example, the js for page display initialization must be placed in the head, because the initialization must be done in advance (such as setting css for the page body, etc.); and if the function is executed through an event call, there is no requirement for the location.

4. JavaScript-comments are very important

Comments are used to improve the readability of the code. Comments are divided into two types:

Single-line comments , add the symbol "//" before the comment content. Multi-line comments start with "/" and end with "/".

5. Use the keyword var to define variables. The syntax is as follows:

var variable name

The variable name can be named arbitrarily, but it must be followed Naming rules:

1. Variables must start with a letter, underscore (_) or dollar sign ($).

2. Then you can use any number of English letters, numbers, underscores (_) or dollar signs ($).

3. JavaScript keywords and JavaScript reserved words cannot be used.

Note: 1. JS is case-sensitive. If the variables mychar and myChar are different, it means they are two variables. 2. Although variables can be used directly without declaring them, they are not standardized and need to be declared first and then used.

6. What is a function

A function is a set of statements that complete a specific function. The basic syntax is as follows:

function function name(){

function code;

}

Explanation: 1. functionThe key to defining a function Character. 2. "Function name" is the name you give the function. 3. Replace "function code" with code that completes a specific function.

Function call: After the function is defined, it cannot be executed automatically, so you need to call it. Just write the function directly where you need it,

7. JavaScript output content: use document.write()

8. JavaScript -alert message dialog box, alert pops up the message dialog box (including an OK button)

Nine javaScript --confirm (confirm message dialog box)

confirm(str);

Parameter description:

When the user clicks the "OK" button, return true When the user clicks the "Cancel" button, return false

Note: Pass the return value Can determine what button the user clicked.

10. JavaScript - Question (prompt message dialog box)

prompt pops up a message dialog box, usually used to ask for some information that needs to be interacted with the user. Pops up a message dialog box (including an OK button, a cancel button and a text input box)

Syntax:

prompt(str1, str2);

Parameter description:

str1: The text to be displayed in the message dialog box cannot be modified str2: The content in the text box can be modified

Return value:

1. Click the OK button, and the content in the text box will be used as the function return value 2. Click the Cancel button, and null will be returned

11. Close the window

1. window.close() //Close this window

2. .close(); / /Close the specified window

The above are the most basic usages of Javascript that I have compiled. I hope it can give some new people a basic understanding of Javascript.