Lesson 17 / 28

Basic Validation

Built-in attributes that check input before submit.

required, pattern, min, max

The browser blocks submission and shows a message until these constraints are met.

<input type="text" required minlength="3">
<input type="number" min="1" max="10">
<input type="text" pattern="[A-Za-z]+" title="Letters only">

Not a security fence

HTML validation runs in the browser and can be bypassed — always re-validate on the server too.

Quick check: Which attribute makes a field mandatory before submit?

  • required
  • placeholder
  • readonly
Answer

required — `required` blocks form submission until that field has a value.