验证输入字段以进行人体测试

I am new in java script .any help to validate these to number.

<div class="col-md-12 form-group"><?php 
                                $a_con=rand(0,9);
                                $b_con=rand(0,9);
                            ?>
             Human Test <?php echo $a_con." + ".$b_con?> = 
                            </div>
              </div>
              <div class="row">
             <div class="col-md-12 form-group"><input type="text" value="" placeholder="Human Test" class="form-control" name="value_num" required/>
        <input class="input" name="captcha_num_hidden_contact" id="captcha_num_hidden_contact" type="hidden" value="<?php echo $a_con+$b_con;?>"/>


    </div>