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# Dynamic web pages with JavaScript

Web developers usually talk about three languages that are used to create web pages: HTML, CSS, and JavaScript.
-The HTML: gives the page structure and adds semantics.
-The CSS: enhances the HTML page with rules that state how the HTML content is presented (backgrounds, borders, box
dimensions, colors, fonts, etc.).
-JavaScript: where we can change how the page behaves, adding interactivity. We will aim to keep as much of our JavaScript as possible in separate files.
![image](https://brytdesigns.com/wp-content/uploads/2019/12/html_css_javascript_infographic.png)
## LINKING TO A JAVASCRIPT FILE FROM AN HTML PAGE:
- <script src="app.js"> </script>.
- Javascript run where it found in the HTML.
## STATEMENTS:
JavaScript statements often start with a statement identifier to identify the JavaScript action to be performed. Statement identifiers are reserved words and cannot be used as variable names (or any other things).
* note that:
• Each of the lines of code in green is a statement.
• The pink curly braces indicate the start and end
of a code block. (Each code block could contain
many more statements.)
• The code in purple determines which code
should run
• JAVASCRIPT IS CASE SENSITIVE
JavaScript is case sensitive so hourNow means
something different to HourNow or HOURNOW.