How to introduce Javascript code in HTML

Javascript is a scripting language widely used in web development. It can be run in web pages to make them more dynamic and interactive. To use Javascript in a web page, we need to connect it with HTML. This article will introduce how to introduce Javascript code in HTML and use it to change the appearance and behavior of web pages.

1. What is Javascript?

Javascript is a lightweight scripting language used to add dynamic effects and interactivity to web pages. It is an interpreted language, unlike traditional compiled languages. Javascript code does not require a compiler to be converted into executable code, it is executed instantly when the web page loads. Because Javascript can be executed on the client side, communication with the server is reduced and allows for faster responses and a smoother user experience.

2. How to introduce Javascript?

In order to use Javascript in a web page, we need to introduce it into the HTML file. There are three ways to introduce Javascript code into HTML files:

Inline script Inline script refers to embedding Javascript code directly in the HTML page. method. Javascript code can be written into HTML files using the tag.

Inline Script Hello World!

alert('Welcome to Javascript!');

In the above code, we have embedded a script in the HTML file to display an alert box to the user. However, this approach makes the code difficult to maintain and may negatively impact the performance of the web page. Therefore, the use of inline scripts is not recommended.

Internal script Internal script refers to writing Javascript code in the HTML file, but not in the HTML tag. You can use the tag to place Javascript code within a tag within a or tag.

Internal Script function welcome(){ alert('Welcome to Javascript!'); } Hello World! In the above code, we put the Javascript code in the tag inside the tag and defined a function called welcome. This function is called in the onload event in the tag. This is a better approach, but still not perfect.

External scripts The best way is to store Javascript codes in external files and link to them from the HTML file. Create a separate file for the external Javascript file and save it with a .js extension. The file can then be referenced using the tag.

Assuming we save the above Javascript code in a file called "welcome.js", we can use the following code to connect it to the HTML file:

External Script Hello World! In the above code , we use the src attribute of the tag to link the "welcome.js" file into the HTML file. Then, we call the welcome() function in the onload event inside the tag.

The benefit of using external scripts is that it makes Javascript code easier to maintain and update, and HTML files easier to read and manage. Additionally, it caches files, thereby improving the performance of your website.

3. Manipulate HTML elements in Javascript

Once Javascript is introduced into the HTML file, we can use it to manipulate HTML elements. HTML elements can be accessed and modified using the Document Object Model (DOM).

DOM is an API for accessing and manipulating elements in HTML and XML documents. It treats the document as a tree structure, in which each element is a node, and HTML elements are accessed and modified by operating nodes. The following are some common DOM methods:

getElementById(): Get an element by ID. getElementsByTagName(): Get elements by tag name. getElementsByClassName(): Get elements by class name. innerHTML attribute: Gets or sets the content of the element. style attribute: Get or set the style attribute of the element. The following is an example of using DOM methods to change HTML elements:

DOM Manipulation function changeColor(){ document.getElementById("text").style.color = "red"; } Hello World! Change Color In the above code, we have defined a title in and created a button. In the JavaScript function changeColor(), we use getElementById() to get the element with the ID "text" and change its text color to red.

4. Summary

Javascript is a popular language used for web development, which can make web pages more dynamic and interactive. To use Javascript in HTML files, you can use inline scripts, internal scripts, or external scripts. External scripting is the best approach as it makes the code easier to maintain and read, and improves the performance of the website. Once Javascript is attached to the HTML file, we can use DOM methods to access and modify HTML elements.