JS原生方法getAttribute(required)获取值实例页面

CSS代码：

.demo pre{display:inline; margin:0;}
.co{color:#f30;}
.demo p{margin-top:2px;}
                

HTML代码：

<div class="demo">
    <pre>&lt;input id="input1" required /></pre> → <input id="input1" required />
    <p><code>$("input1").getAttribute("required")</code> → <span id="result1" class="co"></span></p>
    <pre>&lt;input id="input2" /></pre> → <input id="input2" />
    <p><code>$("input2").getAttribute("required")</code> → <span id="result2" class="co"></span></p>
</div>
                

JS代码：

var $ = function(id) {
    return document.getElementById(id);
};
for (var i=1; i<=2; i++) {
    var required = $("input" + i).getAttribute("required");
    if (required === "") {
        required = "空字符串";
    }
    $("result" + i).innerHTML = required + "";
}