References

Beginner-friendly references for web development, with live, editable examples.

The HTML oninput event

Event All modern browsers Updated
Quick answer

The HTML oninput attribute runs JavaScript when the value of an <input>, <textarea> or contenteditable element changes. It is an inline handler for the input event; in modern code prefer addEventListener('input', …).

Overview

The oninput event attribute runs JavaScript every time an input value changes. In JavaScript the event itself is named input. Drop the on prefix when you call addEventListener.

It is a form-related event, fired by form controls such as <input>, <select> and <textarea> (or the <form> itself) as the user interacts with them and as data is submitted or validated.

You can wire this up with the inline oninput HTML attribute, but the modern, recommended approach is element.addEventListener('input', handler) in JavaScript. That keeps behavior out of your markup, lets you attach several handlers to the same event, and makes them easy to remove. The inline attribute is fine for quick demos.

Syntax

<element oninput="handler()">…</element>

element.addEventListener('input', handler);

Example

Live example 
<input oninput="this.nextElementSibling.textContent = this.value.length + ' chars'" placeholder="Type…" style="padding:8px;"><span></span>

Best practices

  • Prefer element.addEventListener('input', handler) over the inline oninput attribute; it separates behavior from markup and allows multiple handlers.
  • Use native form validation (required, type, pattern) alongside JavaScript, not instead of it.
  • Re-validate on the server too; client-side events can be bypassed.
  • Give every control a <label> so the interaction is accessible.

Frequently asked questions

What is the oninput event?
It runs JavaScript every time an input value changes. In JavaScript the event is named input.
What is the difference between oninput and onchange?
oninput fires on every keystroke as the value changes; onchange fires once the value is committed (often on blur).
Should I rely on form events for validation?
Use them for instant feedback, but always validate again on the server, since client-side checks can be bypassed.
Should I use the oninput attribute or addEventListener?
Prefer element.addEventListener('input', …) in JavaScript. The inline oninput attribute works but mixes behavior into the markup and allows only one handler per element.
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