Tutorial: Write Your First JavaScript Program
Husband. Father. Software engineer @MITREcorp. Lecturer. Helping you code. The opinions expressed in this blog are my own. #JavaScript #NodeJS #Java #Python
JavaScript programs execute in the browser. That means you need an HTML document. Here is a simple one to start with:
<!DOCTYPE html>
<html lang="en">
<head>
<title>My document</title>
</head>
<body>
</body>
</html>
That is a very basic HTML document that doesn’t do much. For now, save it to a file named helloworld.html. The .html extension indicates that the file is an HTML document.
Now add JavaScript to the HTML document. Write JavaScript code inside a <script> </script> element:
<!DOCTYPE html>
<html lang="en">
<head>
<title>My document</title>
</head>
<body>
<script>
let s = "Hello, world.";
document.write(s);
console.log(s);
</script>
</body>
</html>
This JavaScript code declares a variable s and assigns the string "Hello, world." to it.
Next, it outputs s to the document.
Finally, it outputs s to the console.
To execute the JavaScript code, double-click the helloworld.html file. The program will execute in your browser. Note the output in the body of the document.
To see the console output, view the browser console:
- Right-click anywhere in the document and click Inspect.
- Expand the browser window wide.
- Click the Console tab in the top-right.
🏆 Congratulations! That’s your first JavaScript program!
Now you can explore and learn the rest of the JavaScript language.
Follow me on Twitter @realEdwinTorres for more programming tips. 😀