How do you write a javascript program to run?
In order to follow along with this course, you need to know how and where you run your JavaScript code. You have several options to run your first hello world programming: Show
Open your editor and create a file named file_type_js_official index.js
How to Run JavaScript from the Command LineRunning a JS program from the command line is handled by NodeJS. Start by installing NodeJS on local machine if necessary.
Now simply open the command line in the same directory as
the command line
How to Run JavaScript from the BrowserWhen people think of “JavaScript”, they most often think of a web browser. You can run code in the browser by creating an HTML file that references the script. In our case, we used the Run a script from an HTML filefile_type_html index.html
Now simply open this HTML file on your local machine and open the developer console (next step) to see the output. Inspect the Browser ConsoleIn Chrome, you can open the developer console with Output of the browser console in Chrome Run JavaScript with a FrameworkIt is worth mentioning that frameworks like React, Angular, Svelte, etc will take care of the building & running of your app automatically and provide framework-specific tooling and steps for running code. In the real world, you are more likely to use the tooling provided by the framework to run your code, as opposed to the basic methods shown in this couse. Run JavaScript in a SandboxThis course uses StackBlitz to run JS code examples in an isolated sandbox in the browser. This is a great option for sharing quick demos and issue reproductions 💡. Being a client-side scripting language, JavaScript needs some clients to interpret and execute it. In the case of web applications, we can use any of the supported web browsers as a platform for executing JavaScript. In the below sections, let's understand how does JavaScript run in a web browser and how the JavaScript engine interprets the JavaScript code. Moreover, we will also understand how JavaScript can integrate under various sections of an HTML page.
How does JavaScript run in a web-browser?JavaScript is an interpreted language where code is explained and executed at the runtime. Additionally, we know that web browsers understand HTML and CSS and converting those languages into a visual display on the screen. The part of the web browser that understands HTML and CSS is called the rendering engine. However, most browsers also have a JavaScript interpreter. That’s the part of the browser that understands JavaScript and run JavaScript programs. A typical architecture of a browser looks like below: As we can see, the browser's Rendering engine interacts with the "JavaScript's Interpreter" and
sends the JavaScript code to the JavaScript engine for processing.
Now when we talk about JavaScript engines, each of the browsers have their pre-installed engines. Below are few of the JavaScript engines developed and used by some major browsers:
How to embed and run JavaScript in a web-browser?The web browser is usually expecting HTML, so you must specifically tell the browser when JavaScript is coming by using the How to embed and execute JavaScript in the HTML tag?The The below code demonstrate the “Hello world!” program using JavaScript written directly inside
Open any text editor like notepad++ and type the above code. Save the file with name helloworld.html and open it in any browser (Chrome, Firefox, or IE). It should show the output as: As seen in the above example, "document.write" is a function used to write data into the Html page. When we open an Html file in the browser, the JavaScript present under script tag executes. We will discuss more details above other functionalities, like write in the DOM Manipulation article. How to embed and run JavaScript in HTML tag?The The below code demonstrate the “Hello world!” program using JavaScript written under the
Write the above code in a text editor and save the file with the name helloworld2.html. Later open it in any browser. In the above example, we created a function in the header and called that function in the body tag. At this moment, don't worry about what is a function and it's usage because we will cover it in functions article. How to embed an external JavaScript file in HTML?Apart from the above ways of integrating JavaScript in the HTML, we can save the JavaScript as a separate script file with .js extension and include the same inside the HTML code using the src attribute of the The below code demonstrates the “Hello world!” program using JavaScript written as an external file.
Save the above JavaScript code as ext.js file. Invoke the above JavaScript in the below HTML using the src attribute of
Note: The src attribute will specify the absolute path of the JavaScript file. In the above example, we have created javascript in a separate file and used that file in Html with the help of an src tag, which imports JavaScript code in the provided file at runtime. How to diagnose an error in JavaScript?When the website loads but does not display correctly, this is due to a coding error on the site. Usually, JavaScript causes it or CSS errors. If you have JavaScript on your website that is not working, you can diagnose them by using your browsers "Error Console". Each browser has a built-in “Error Console” for diagnosing scripting errors on your site. To understand the "Error Console" in detail, let's consider the code snippet below. Whereby we have explicitly introduced an error by removing the double quotes from the string "Hello World!" while passing the same to the document.write() method:
Save the file with name firstProgramWithError.html and open it in a browser. It should show the output as: As we can see from the above screenshot that nothing is there on the HTML page. As a result, this makes it skeptical that there's something wrong, as the output is not as expected. So, how to check what the error is? One can check this error with the help of the browser's "Error Console". Let's consider we are using "Chrome" viewing our program. So, we can open the "Error Console" in chrome using the following steps to view the error raised by our program: 1. Firstly, Right-click anywhere in the browser's viewport to open the context-menu as below: 2. Secondly, click on the "Inspect" item in the Context Menu." It will open chrome-dev tools. Select the "console" tab as highlighted in below screenshot: 3. Finally, if we again open the above firstProgramWithError.html file in chrome, it shows the output as below: 4. So, it shows the error in the "Console" tab and mentions the error is in "line 8" of the file. Therefore, a user can quickly diagnose any error, if there, in the JavaScript code. Similarly, other browsers also provide the "Error Console" windows. Which, in turn, diagnose the JavaScript errors whenever an error arises in a specific code of JavaScript. Key Takeaways
Let's now move to the next article where we will learn about concepts of data types and variables in JavaScript. How do you write and run a JavaScript code?To execute JavaScript in a browser you have two options — either put it inside a script element anywhere inside an HTML document, or put it inside an external JavaScript file (with a . js extension) and then reference that file inside the HTML document using an empty script element with a src attribute.
How do I create a JavaScript file to run?Example 1: Create a JavaScript file. Name this file as New.. Open Terminal or Command Prompt.. Set Path to where New. js is located (using cd).. Type “node New. js” and press ENTER.. How do I run the first JavaScript program?To run JavaScript on a browser,. Open your favorite browser (here we will use Google Chrome).. Open the developer tools by right clicking on an empty area and select Inspect. Shortcut: F12 . Inspect Browser.. On the developer tools, go to the console tab. Then, write JavaScript code and press enter to run the code.. What are the steps needed to create and run a simple program using JavaScript?Your First JavaScript Program. In your favorite text editor, open the file hello. ... . Click in the empty line just before the closing tag and type: . ... . Launch a web browser and open the hello.. |