我有几个输入字段和验证。首先，“提交”按钮将被禁用。每次我输入字段时，验证功能都会立即起作用。在每个字段都填充了有效输入后，我想启用“提交”按钮，但是我尝试了以下一些代码，该代码不起作用。

if($('input').val() == true) {
           $('.myButton').prop("disabled",false);
        }

请帮助

jsfiddle

JS

function validateForm() {
    val = true;
    var firstName = $('#firstname').val();
    if (!firstName) {
        $('#firstname').siblings(".error").addClass('alert-on');
        val = false;
    }
    var lastName = $('#lastname').val();
    if (!lastName) {
        $('#lastname').siblings(".error").addClass('alert-on');
        val = false;
    }

    var input = $('#email');
    var re = /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/;
    var is_email = re.test(input.val());
    if (!is_email) {
        $('#email').siblings(".error").addClass('alert-on');
        val = false;
    }

    return val;
}
$(function () {
        $('.myButton').prop("disabled",true);
    $("input").on("change keyup paste",function () {
        if (!$(this).val()) { $(this).siblings('.error').addClass('alert-on'); }
        else { $(this).siblings('.error').removeclass('alert-on'); }
    });
        if($('input').val() == true) {
        $('.myButton').prop("disabled",false);
    }
    $("#form").submit(function (event) {
        if (validateForm()) {
            return;
        };
        event.preventDefault();
    });

})

HTML

<form id="form">
        <div class="">
            <input type="text" placeholder="First name*" id="firstname">
            <div class="error">Required</div>
        </div>
        <div class="">
            <input type="text" placeholder="Last name*" id="lastname">
            <div class="error">Required</div>
        </div>
        <div class="">
            <input type="email" id="email" name="email" placeholder="email">
                <div class="error">A valid email address is required</div>  
        </div>
        <div class="">
            <input type="text" placeholder="Phone*" maxlength="12" id="phone">
            <div class="error">Required</div>
        </div>

        <div id="form_submit">
            <button class="myButton" type="submit">
                Submit
            </button>
        </div>
</form>

CSS

input {
  display: list-item;
  margin-bottom: 10px;
}
.error {
  display: none;
  color: red;
}
.alert-on {
  display: block;
}

.myButton{
  height: 40px;
  width: 90px;

}