How to Run JavaScript

By Xah Lee. Date: . Last updated: .

There are 3 major ways to run JavaScript code.

Following are details of each.

Embedding JavaScript in HTML

To evaluate a piece of JavaScript code, you need to put JavaScript code in a HTML file and view the file in browser.

Here's how to embed JavaScript into HTML. Put the following into a file:

<script>
alert("hi!");
</script>

For example, name the file test.html. Then, open it in a browser.

If you have more than a few lines of JavaScript code, you can put the JavaScript code in a dedicated file, like this:

<script src="test2.js"></script>
  1. Create a file named test2.html, with the above content.
  2. Create a file named test2.js, with the content alert("hi2");.
  3. Open the file test2.html in browser.

Note: older tutorial may say to have “type” attribute like this:

<script type="text/javascript">…</script>

or

<script type="text/javascript" src="…"></script>

But the type attribute is not necessary since html5.

Use Browser's Web Developer Console

chrome js console 2016-10-27
Google Chrome browser web JavaScript console.

A good way to learn JavaScript is to run it in browser's JavaScript console.

See: JS: How to Use Browser Console.

Using node.js

Another good way to test JavaScript code is “node.js”. With node.js, you can run JavaScript like a shell script in terminal.

Download it at http://nodejs.org/.

On Linux, you can also install by sudo apt-get install nodejs, but that is usually much older version, as nodejs moves fast.

You can run it interactively. Type node to start the interactive prompt. Type 【Ctrl+d】 to exit.

nodejs repl
node.js REPL

You can also run it as shell script.

For example, create a file named myscript.js, then put this in the content:

console.log(2+3);

Then, you can run the script in shell like this: node myscript.js. (For emacs users, you can eval the JavaScript code in a buffer directly. See: Emacs Lisp: a Command to Execute/Compile Current File)

JavaScript Basics

  1. JavaScript Basics
  2. Value Types
  3. true, false
  4. Operators
  5. Variable
  6. if then else
  7. for while do Loop
  8. Array Basics
  9. Object Basics
  10. RegExp Tutorial
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