Last modified on 22 May 2014, at 03:42

JavaScript/First Program

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Here is a single JavaScript statement, which creates a pop-up dialog saying "Hello World!":

alert("Hello World!");

For the browser to execute the statement, it must be placed inside a <script> element. This element describes which section of the HTML code contains executable code, and will be described in further detail later.

<script type="text/javascript">
  alert("Hello World!");
</script>

The <script> element should then be nested inside the <head> element of an HTML document. Assuming the page is viewed in a browser that has JavaScript enabled, the browser will execute (carry out) the statement as the page is loading.

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Some Page</title>
    <script type="text/javascript">
      alert("Hello World!");
    </script>
  </head>
  <body>
    <p>The content of the web page.</p>
  </body>
</html>

This basic hello world program can then be used as a starting point for any new programs that you need to create.

ExercisesEdit

Exercise 1-1Edit

Copy and paste the basic program in a file, save it on your hard disk as "exercise 1-1.html". You can run it in two ways:

  1. By going to the file with a file manager, and opening it using a web browser (e.g. in Windows Explorer it is done with a double click)
  2. By starting your browser, and then opening the file from the menu. For Firefox, that would be: Choose File in the menu, then Open File, then select the file.

What happens?

Answer

A dialog appears with the text: Hello World!

Exercise 1-2Edit

Save the file above as "exercise 1-2.html". Replace the double quotes in the line alert("Hello World!"); with single quotes, so it reads alert('Hello World!'); and save the result. If you open this file in the browser, what happens?

Answer

Nothing changes. A dialog appears with the text: Hello World! The double quotes and the single quotes are equivalent.


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