纯CSS3实现表单验证效果(非常不错)

<form>
 <ol>
   <li>
     <label for="tel">Tel:</label>
     <input type="tel" required name="" pattern="\d{11}" id="tel">
   </li>
   <li>
     <label for="url">Website:</label>
     <input type="url" required name="" id="url">
   </li>
   <li>
     <label for="email">Email:</label>
     <input type="email" required name="" id="email">
   </li>
   <li>
     <input type="submit" name="" value="Send the form">
   </li>
 </ol>
</form>

* {
    margin: 0;
    font: 13px tahoma, verdana, sans-serif;
    padding: 0;
}
ol {
    width: 400px;
    margin: 50px;
}
li {
    clear: both;
    list-style-type: none;
    margin: 0 0 10px;
}
li:nth-last-child(1) {
    text-align: center;
}
label {
    display: block;
    float: left;
    margin: 0 10px 0 0;
    padding: 5px;
    text-align: right;
    width: 100px;
}
input {
    border-radius: 5px;
    padding: 5px 5px 5px 30px;
    width: 155px;
}
input:focus {
    outline: none;
}

input:invalid:required {
    background-image: url('nor.png');
    box-shadow: 0 0 5px #f0bb18;
    border: 2px solid #f0bb18;
}

input:focus:invalid {
    background-image: url('warn.png');
    box-shadow: 0 0 5px #b01212;
    border: 2px solid #b01212;
}

input:valid {
    background-image: url('suc.png');
    border: 2px solid #7ab526;
}

input[type="submit"] {
    background: #7ab526;
    border: none;
    box-shadow: 0 0 5px #7ab526;
    color: #fff;
    cursor: pointer;
    font-weight: bold;
    padding: 7px;
    width: 150px;
}

<form novalidate>
    ...
</form>

<form>
    ...
    <input type="submit" formnovalidate>
</form>

<form>
    <input oninput="check()" type="tel" id="tel">
</form>
<script>
    function check() {
        tel = document.querySelector('#tel');
        tel.setCustomValidity('请输入正确的11位电话号码');
    }
</script>

tel = document.querySelector('#tel');
console.log( tel.validity )

function check( el ) {
    var validity = el.validity;
    if ( validity.valueMissing ) {
        el.setCustomValidity('该字段为必填内容');
    } else if ( validity.patternMismatch ) {
        el.setCustomValidity('输入内容不符合格式');
    } else {
        el.setCustomValidity('输入有误');
    }
}

console.log( el.validationMessage )
// "请填写此字段。"