document.getElementsByClassName 用法

尝试隐藏下面全部ＤＩＶ

<div id="div1" class="opt" style="display: none">SHOW</div><div id="div2" class="opt" style="display: none">SHOW</div><div id="div3" class="opt" style="display: none">SHOW</div>

先在body 新增input

<input name="name" type="button" onClick="show();" value="显示"><input name="name" type="button" onClick="hiddens();" value="隐藏"><div id="div1" class="opt" style="display: none">SHOW</div><div id="div2" class="opt" style="display: none">SHOW</div><div id="div3" class="opt" style="display: none">SHOW</div>

最后加上ＪＳ

var s = document.getElementsByClassName('opt');function show(){    // var s = document.getElementsByClassName('opt');    for(var i = 0;i<s.length;i++){    s[i].style.display="";    }};function hiddens(){    // var s = document.getElementsByClassName('opt');    for(var i = 0;i<s.length;i++){    s[i].style.display="none";    }};