Kerala Plus Two Computer Science (DHSE): Web Technology: HTML, CSS and JavaScript

Web Technology: HTML, CSS and JavaScript

The exam tests document structure, presentation rules, and client-side behaviour, including form validation.

HTML

• HTML describes structure with elements and attributes: <html>, <head>, <body>, headings, lists, links, images, tables, forms.
• Attributes use name='value'; tags nest properly.
• Forms collect input; action sends data to a server, method is usually GET or POST.

CSS

• CSS controls presentation. Three placements: inline (style attribute), internal (<style>), external (.css linked with <link>).
• Selectors: element, .class, #id. Specificity order: inline > id > class > element.
• Box model: content, padding, border, margin.

JavaScript

• Runs in the browser; adds interactivity and validation.
• Variables via let/const; functions; DOM access with document.getElementById().
• Events such as onclick, onsubmit, onchange; return false from a handler can cancel submission.

Worked example

A form field id='age' is validated on submit: read let a = document.getElementById('age').value; then if (a === '' || isNaN(a)) { alert('Enter a number'); return false; }. Reasoning: value is a string; isNaN checks numeric validity; returning false stops the form from being sent, so invalid data never reaches the server.

Traps

• Using = instead of === in conditions.
• Assuming JavaScript runs on the server; it runs client-side here.
• Expecting CSS id selectors to be written with .; ids use #.
• Placing <script> before the elements it accesses without handling load order.
• Relying only on client-side validation; server-side validation is still required.