javascript - check if input value not equal to integer then don't submit form -

i have simple php email form, getting spam emails. have added check input, user have fill input. if input value equal 12 submit form, otherwise don't submit form popup error.(please math.)

<form action="" method="post"> <input type="text" name="name" placeholder="name" required> <input type="text" name="email" placeholder="email" required> <input type="text" name="phone" placeholder="phone" required>  <div class="check">    <label>6 x 2 =</label>    <input type="text" name="not_robot" required="required"> </div>  <input type="submit" value="submit"> </form> 

i using php method below:

if(isset($_post['not_robot']) !== 12 && isset($_post['not_robot']) !== ''){     echo '<script type="text/javascript">alert("please math, if human.");</script>'; }else{     //email script here } 

when submit form, error popup appear saying "please math, if human", after close popup, send email. appreaciated thanks

p.s: if check method possible using javascript or jquery great help.

try check when submitting form. go below code or link-

jsfiddle

html code-

<form action="" method="post">   <input type="text" name="name" placeholder="name" required>   <input type="text" name="email" placeholder="email" required>   <input type="text" name="phone" placeholder="phone" required>    <div class="check">     <label>6 x 2 =</label>     <input type="text" name="not_robot" required="required">   </div>    <input type="submit" value="submit"> </form> 

javascript code-

$('form').submit(function() {       if (parseint($('input[name="not_robot"]').val()) == 12) {         return true;       }       else{         alert('you not enterd correct value');         return false;       }     });