# Validate input with a component's validate()
> Implement validate() in a component, read the invalid, touched and modified states, and find invalid fields with ERRORS().
Framework: jcomponent20
Product: jComponent 20 (jcomponent@20)
Language: en
Content-SHA256: da083e2d978ec1a4472abb4b2d8a9ae7b2b3d28b560d6e54ea3a9114ed7be5f7
Snapshot: c0700e321579725c5cf4f5ace1ad7d2866d1b4f93c24a63c0b41b6b7998e976c
Sources: jcomponent20@3fedd009a277f50fddc608b97afbec553b67c51b
Review: not-recorded
A component that edits a value can validate it. Define `self.validate(value)` and return `true` (or an empty string) when the value is valid, or `false` (or a message) when it is not. Write the value back with `self.modify(value)`: it also marks the component as **modified** and **touched**.
jComponent keeps these states in `config` (`invalid`, `touched`, `modified`) and as CSS classes (`ui-invalid`, `ui-touched`, `ui-modified`), so styling needs no code. `ERRORS(path, callback)` returns the invalid components below a path, which is what a form needs before it submits, and `RESET(path)` clears the touched and modified states.
```html public/index.html
jComponent
```