# Element “script” must not have attribute “defer” unless attribute “src” is also specified. > Canonical HTML version: https://rocketvalidator.com/html-validation/element-script-must-not-have-attribute-defer-unless-attribute-src-is-also-specified > Attribution: Rocket Validator (https://rocketvalidator.com) > License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) The `defer` and `async` boolean attributes control how and when an external script is fetched and executed relative to HTML parsing. These attributes exist specifically to optimize the loading of external resources. An inline ` ``` This triggers the validation error because `defer` is present without a corresponding `src` attribute. ### ✅ Fix option 1: Add a `src` attribute Move the JavaScript into an external file (e.g., `app.js`) and reference it: ```html ``` The browser will download `app.js` in parallel with HTML parsing and execute it only after the document is fully parsed. ### ✅ Fix option 2: Remove `defer` from the inline script If the script must stay inline, simply remove the `defer` attribute: ```html ``` ### ✅ Fix option 3: Use `DOMContentLoaded` for deferred inline execution If you need your inline script to wait until the DOM is ready, wrap the code in a `DOMContentLoaded` event listener: ```html ``` This achieves a similar effect to `defer` but is valid for inline scripts. ### ❌ Invalid: `async` on an inline script The same rule applies to `async`: ```html ``` ### ✅ Fixed ```html ``` Or simply remove `async` if the script is inline: ```html ```