How to run javascript code

Javascript is a very popular programming language that is widely used in web development and dynamic interaction. This article will explain how to run Javascript code in different environments, including browsers, Node.js, and command line interfaces.

1. Running Javascript code in the browser

Running Javascript code in the browser is the most common application scenario. Generally speaking, Javascript code can be run in the following two ways.

1. Embedded

In HTML files, Javascript code can be embedded through the <script> tag, as shown below: </script>

nbsp;html>


    <title>内嵌式</title>


    <script>
        // Javascript代码
        alert("Hello World!");
    </script>

In browsing Open the HTML file in your browser and you will see a dialog box pop up, displaying "Hello World!".

2. External

Store the Javascript code in a separate .js file, which is introduced through the src attribute of the <script> tag, as shown below: </script>

nbsp;html>


    <title>外部式</title>

    <script></script>


    <!-- 此处可以留空  -->

Create an app.js file in the same directory of the HTML file, which contains Javascript code, as shown below:

alert("Hello World!");

Similarly, open the HTML file in the browser, A dialog box will pop up, displaying "Hello World!".

2. Running Javascript code in Node.js

Node.js is a platform for writing server-side applications using Javascript. It is different from Javascript in the browser because it does not have a DOM and BOM, but it supports functions such as file operations and network requests, making it possible to process server-side data through Javascript.

There are two ways to run Javascript code in Node.js.

1. REPL mode

REPL is the command line interactive environment that comes with Node.js, which can run Javascript code directly. In the command line terminal, enter the following command to enter REPL mode:

$ node

Then, you can enter the Javascript code and press the Enter key to execute the code, as shown below:

$ node
> console.log("Hello World!");
Hello World!

2. Introduce in the file

Store the Javascript code in a .js file, and then execute the file through the command line to run the Javascript code in Node.js. For example, create a file named app.js and write the following code in it:

console.log("Hello World!");

In the command line terminal, enter the directory where the file is located and enter the following command to run the file:

$ node app.js

The execution results are as follows:

$ node app.js
Hello World!

3. Run Javascript code in the command line interface

In addition to running Javascript code in the browser and Node.js, you can also run the Javascript code in the command line interface Run Javascript code in the line interface. Here are two methods.

1. V8 engine

V8 is the Javascript engine used by Google Chrome browser. It can also be run independently in the command line. Use the following steps to run Javascript code.

First, you need to download the source code of the V8 engine from the official website. After the download is completed, enter the directory of the V8 engine and execute the following command to compile:

$ make native

After the compilation is completed, enter the out/native/ directory and execute the following command to start the command line environment of the V8 engine:

$ ./d8

Next, you can enter the Javascript code and press the Enter key to execute the code, as shown below:

$ ./d8
V8 version 9.0.257 (candidate)
d8> print("Hello World!");
Hello World!

2. js command

Node installed on the machine In .js, there is a command specifically used to run Javascript code on the command line, which is called js. Follow the steps below to run Javascript code.

In the command line terminal, enter the following command to enter the REPL mode:

$ js

Then, you can enter the Javascript code and press the Enter key to execute the code, as shown below:

$ js
print("Hello World!");
Hello World!

This article explains how to run Javascript code in different environments, including browsers, Node.js, and command line interfaces. These methods can help us better apply Javascript technology and implement more complex, efficient and multifunctional applications.

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