With this code snippet, you will be able to verify user's email address and prevent them from submitting an incorrect one. User will also be unable to submit the form by pressing the Enter key. Scroll up and click on the demo link to see how code is working in real world, clone the project and modify however you want. You can also check how code was added to page.
On line 2, input element has an ID of form-input, that you can modify, as well as hidden submit button with ID of form-submit. When email is verified, the submit button appears. Code for disabling enter key starts on line 23.
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<p> CODE: https://gist.github.com/martinhudobivnik/d24062e9b1b95ae69c103e8a8ebc2e0f.js</p>