Disable spell-checking on HTML textfields

Question

Update: As suggested by a commenter (additional credit to How can I disable the spell checker on text inputs on the iPhone), use this to handle all desktop and mobile browsers.

<tag autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/>

Original answer: Javascript cannot override user settings, so unless you use another mechanism other than textfields, this is not (or shouldn't be) possible.

Yes, use spellcheck="false", as defined by HTML5, for example:

<textarea spellcheck="false">
    ...
</textarea>

For Grammarly you can use:

<textarea data-gramm="false" />

An IFrame WILL "trigger" the spell checker (if it has content-editable set to true) just as a textfield, at least in Chrome.

The following code snippet disables it for all textarea and input[type=text] elements:

(function () {
    function disableSpellCheck() {
        let selector = 'input[type=text], textarea';
        let textFields = document.querySelectorAll(selector);

        textFields.forEach(
            function (field, _currentIndex, _listObj) {
                field.spellcheck = false;
            }
        );
    }

    disableSpellCheck();
})();