JSFiddle - React, Tailwind, and code Playground

HTML

<form action="http://google.com" name="testForm" id="latest">
    <div>
        <label for="confirm" class="fixedwidth">Yes I confirm all my details are correct</label>
        <input type="checkbox" name="confirm" id="latest1" />
    </div>
    <div class="button">
        <input type="submit" value="SUBMIT" />
    </div>
</form>

JavaScript

document.getElementById("latest").onsubmit = function () {
        var send = document.getElementById("latest1"),
            sendValue = send.value,
            sendCheck = send.checked,
            errors = "";

        //validate checkbox
        if (!sendCheck) {
            errors += "Please tick the checkbox as confirmation your details are correct \n";
        }


        //validate other stuff here




        //in case you added more error types above
        //stacked all errors and in the end, show them
        if (errors != "") {
            alert(errors);
            return false; //if return, below code will not run
        }

        //passed all validations, then it's ok
        alert("Your details are being sent"); // <- had a missing " after sent.
        return true; //will submit
    }