javascript - 如何从循环输出中删除字符串 'undefined'？

Question

请帮忙解决问题。

页面(JSFIDDLE)显示4个新闻容器。但在第一个新闻容器输出字符串“未定义”之前。我需要删除字符串“未定义”

html:

<div class="banners__wrap-article" id='sk_wrap_82630'></div>

js:

xmlhttp.onreadystatechange=function(){
    if (xmlhttp.readyState==4 && xmlhttp.status==200){
        document.getElementById('sk_wrap_82630').innerHTML = '<div class="banners__smi2"> \
            <div class="banners__smi2__header"><span class="banners__smi2__header-text">Новости</span></div> \
            ' + cycleItems() + ' \
            </div> \
            <div class="banners__smi2"> \
                <div class="banners__smi2__header"><span class="banners__smi2__header-text"></span></div> \
            </div>';                
    }
}

function cycleItems(){
    var items;
    var massive = JSON.parse(xmlhttp.responseText);

    for (var i = 0; i <= 3; i++) { 
        items = items + constructItem(massive.news[i].url, massive.news[i].img, massive.news[i].title) 
    };

    return items;
}

function constructItem(url, img, title){
    var item;

    return '<div class="banners__smi2__item"> \
                <a href="' + url + '" class="banners__smi2__link"> \
                    <img class="banners__smi2__img" src="' + img + '" alt="" /> \
                    <span class="banners__smi2__title">' + title + '</span> \
                </a> \
            </div>';
}

Answer 1

只需在函数cycleItems()中将变量items初始化为空字符串即可。就像

 var items = '';

检查这个 jsfiddle。

JSFiddle