Don't send form data when to type no in confirm window

Type apple in the input whose name is goods,and type 9 in the input whose name is price,and click submit,now confirm window pop up,whatever your click yes or no,the data will send to price.php.
My expectation:
when you click yes ,the data will send to price.php, when you click no ,the data will not send to price.php,what's wrong for my js?

ob = document.getElementById("submit");
function check(){
    if(document.getElementById("price").value < 10){
        var flag = window.confirm(" are your sure the price is less than 10 ?");
        if(flag){
            return true;
        }else{
            exit;
         }
    }
}
ob.addEventListener("click",check,false);

<form action="price.php" method="post">
<table>
    <tr>
        <td>goods</td>
        <td><input type="text" name="goods"></td>
    </tr>
    <tr>
        <td>price</td>
        <td><input type="text" id="price" name="price"></td>
    </tr>
    <tr><td colspan=2><input type="submit" id="submit"  value="submit"></td></tr>
</table>
</form>

The price.php is simple.

<?php
var_dump($_POST);
?>

The exit below can't prevent form data from sending to price.php.

        if(flag){
            return true;
        }else{
            exit;
         }

It is no use either to change exit; into return false;. It is no use either to change js into below.

ob = document.getElementById("submit");
function check(){
    if(document.getElementById("price").value < 10){
        var flag = window.confirm(" are your sure the price is less than 10 ?");
        if(flag){
            return true;
        }else{
            exit;
         }
    }
}
ob.addEventListener("submit",check,false);

Solution

The traditional way is same as The KNVB did,the key point is <form action="price.php" method="post" onsubmit="return check()"> ,to bind form's attribute onsubmit with function check.

DOM0 level event way,almost the same like the traditional way.

<html>
    <body>
        <form action="price.php" method="post" id="form">
            <table>
                <tr>
                    <td>goods</td>
                    <td><input type="text" name="goods"></td>
                </tr>
                <tr>
                    <td>price</td>
                    <td><input type="text" id="price" name="price"></td>
                </tr>
                <tr><td colspan=2><input type="submit" id="submit"  value="submit"></td></tr>
            </table>
        </form> 
        <script>
            var ob = document.getElementById('submit');            
            ob.onclick =function(){
                if(document.getElementById("price").value < 10){
                    var flag = window.confirm(" are your sure the price is less than 10 ?");
                    if(flag){
                        return true;
                    }else{
                        return false;
                     }
            }
        }
        </script>
    </body>
</html>

What OP expect is the DOM2 level event way.

<html>
    <body>
        <form action="price.php" method="post" id="form">
            <table>
                <tr>
                    <td>goods</td>
                    <td><input type="text" name="goods"></td>
                </tr>
                <tr>
                    <td>price</td>
                    <td><input type="text" id="price" name="price"></td>
                </tr>
                <tr><td colspan=2><input type="submit" id="submit"  value="submit"></td></tr>
            </table>
        </form> 
        <script>
            var ob = document.getElementById('submit');  
            function check(event){
                console.log(ob.type);
                if(document.getElementById("price").value < 10){
                    var flag = window.confirm(" are your sure the price is less than 10 ?");
                    if(flag){
                        ob.submit();
                        return true;
                    }else{
                        event.preventDefault();
                        return false;
                     }
                }
           } 
           ob.addEventListener("click",check);
        </script>
    </body>
</html>

The key points in DOM2 level event way are:

1.when flag is true

if(flag){
    ob.submit();
    return true;
 }

2.when flag is false

else{
    event.preventDefault();
    return false;
}