JSFiddle - React, Tailwind, and code Playground

HTML

<form id="myform" onsubmit="return checkcheckboxes()">task 1
    <input type="checkbox" name="chk1" />
    <br />task 2
    <input type="checkbox" name="chk2" />
    <br />task 3
    <input type="checkbox" name="chk3" />
    <br />
    <br />
    <input type="submit" value="Go to the next task" />
    <br />
    <span id="message"></span>
</form>

JavaScript

function checkcheckboxes() {
    var valid = true;
    var inputs = document.getElementById("myform").getElementsByTagName("input");
    for (var i = 0; i < inputs.length; i++) {
        if (inputs[i].type == "checkbox") {
            if (!inputs[i].checked) {
                valid = false;
                break; // break as soon as it finds an unchecked
            }
        }
    }
    if (!valid) {
        document.getElementById("message").innerHTML = "You must check all boxes to proceed";
    } else {
        document.getElementById("message").innerHTML = "congratulations! you have completed all the tasks completely and <a href='http://www.google.com'>here is the link</a>.";
    }
    return false;
}