小编Car*_*los的帖子

var choices = document.querySelectorAll('li');
var maxWidth = 0;
// read
for (i = 0; i < choices.length; ++i) {
    maxWidth = Math.max(maxWidth, choices[i].offsetWidth)
};

// write
for (i = 0; i < choices.length; ++i) {
    choices[i].style.width = maxWidth + "px";
};

ul{
    margin: 0;
    padding: 0;
    list-style: none;
}
li{
    background: red;
    float: left;
    margin: 5px;
}

<ul>
    <li>first choice</li>
    <li>choice</li>
    <li>This is the wider choice</li>
    <li>other choice</li>
</ul>