JSFiddle - React, Tailwind, and code Playground

HTML

both functions must return true for the form to submit but both functions are called (unlike when the && operator is used)

<form action="subscribe.php" 
onsubmit="return ((form_check(this) + another_script(this))===2);" method="post">
    <input type="text" value="">
<input type="submit" value="click">
</form>

JavaScript

function form_check() {
    alert("form_check");
    return false;
}

function another_script() {
    alert("another_script");
    return true;
}