如何检查是否值/属性JSON数据存在 [英] How to check if a value/property exist in JSON data

问题描述

我使用谷歌图书API接收一个书单，但有时也会出现一些图书条目没有某些键/属性，例如，作者或不具有的缩略图。这样的JavaScript说，物业IM试图访问是不确定的和我的应用程序stucks。

示例<一个href=\"https://www.googleapis.com/books/v1/volumes?q=java&callback=jQuery191012062033754773438_1377508316730&_=1377508316731\"相对=nofollow> JSON数据从包含图书搜索例如keywork的Java

全部链接

<$p$p><$c$c>https://www.googleapis.com/books/v1/volumes?q=java&callback=jQuery191020691258599981666_1377508821982&_=1377508821983

如，当作者缺少

 类型错误：row.volumeInfo.authors未定义
 

我tryied两个解决方案建议

 如果（typeof运算（作者）！=未定义）{}
 

和

 如果（'作者在booksObject）{}
 

但其中非似乎工作，因为他们即使在这个proerty存在不会进入循环。

这就是我称之为

 函数populateListview（书籍）{//遍历每个返回项目
$。每个（books.items，功能（我行）{    //填充每个行中的列表
    VAR htmlString ='＆LT;立GT;＆LT; A HREF =book_details.html ID ='+ row.id +'＆GT;＆LT; IMG SRC =;    htmlString + = row.volumeInfo.imageLinks.thumbnail +'';
    htmlString + ='类=UI丽有拇指​​/＆GT;＆LT; H3＆GT;';
    //检查是否作者在JSON存在
    htmlString + = row.volumeInfo.title +'＆下; / H3＆GT;＆所述p为H.;' + row.volumeInfo.authors [0] +'＆LT; / P＆GT;＆LT; / A＆GT;＆LT; /李＆GT;';    //如果不是在作者补充一个未定义的字符串作者
    的console.log（htmlString）;    //新的HTML追加到列表
    $（'＃book_list'）追加（htmlString）。
}）;$（'＃book_list'）的ListView（'刷新'）;
//刷新列表视图等等新元素被添加到DOM
};
 

解决方案

您可以检查 $ IsArray的（row.volumeInfo.authors）及＆安培; row.volumeInfo.authors.length＆GT; 0

 的console.log（books.toString（））;
//遍历每个返回项目
$。每个（books.items，功能（我行）{    //填充每个行中的列表
    VAR htmlString ='＆LT;立GT;＆LT; A HREF =book_details.html ID ='+ row.id
            +＆GT;＆下; IMG SRC =';    htmlString + = row.volumeInfo.imageLinks.thumbnail +'';
    htmlString + ='类=UI丽有拇指​​/＆GT;＆LT; H3＆GT;';
    如果（$ .isArray（row.volumeInfo.authors）及＆放大器; row.volumeInfo.authors.length大于0）{
        // code为了什么在这里使用JSON做
        htmlString + = row.volumeInfo.title +'＆下; / H3＆GT;＆所述p为H.;'
                + row.volumeInfo.authors [0] +'＆LT; / P＆GT;＆LT; / A＆GT;＆LT; /李＆GT;';
    }其他{
        htmlString + = row.volumeInfo.title +'＆下; / H3＆GT;＆所述p为H.;' +作者Undifined
                +'＆LT; / P＆GT;＆LT; / A＆GT;＆LT; /李＆GT;';
    }    的console.log（htmlString）;    //新的HTML追加到列表
    $（'＃book_list'）追加（htmlString）。
}）;$（'＃book_list'）的ListView（'刷新'）;
//刷新列表视图等等新元素被添加到DOM
 

I am using Google Books API to receive a list of books, but sometimes some book entry does not have some keys/properties, e.g., Authors, or does not have a Thumbnail. Thus JavaScript says that the property im trying to access is undefined and my application stucks.

Example Json data example from a book search containing the keywork Java

Full link

https://www.googleapis.com/books/v1/volumes?q=java&callback=jQuery191020691258599981666_1377508821982&_=1377508821983

E.g., when Authors is missing

TypeError: row.volumeInfo.authors is undefined

I tryied two solutions suggested

if ( typeof (authors) != "undefined"){}

and

if('authors' in booksObject) {}

but non of them seems to work, since they never enter the loops even when this proerty exists.

This is where I call

function populateListview(books) {

//iterate each returned item
$.each(books.items, function(i, row) {

    //populate each row in the list
    var htmlString = '<li><a href="book_details.html?id=' + row.id + '"><img src="';

    htmlString += row.volumeInfo.imageLinks.thumbnail + '"';
    htmlString += 'class="ui-li-has-thumb"/><h3>';
    //Check if authors exists in JSON
    htmlString += row.volumeInfo.title + '</h3><p>' + row.volumeInfo.authors[0] + '</p></a></li>';

    //If not add an undefined authors string in the authors 


    console.log(htmlString);

    //append new html to the list
    $('#book_list').append(htmlString);
});

$('#book_list').listview('refresh');
// refresh the list-view so new elements are added to the DOM
};

解决方案

You can check $.isArray(row.volumeInfo.authors) && row.volumeInfo.authors.length > 0

console.log(books.toString());
// iterate each returned item
$.each(books.items, function(i, row) {

    // populate each row in the list
    var htmlString = '<li><a href="book_details.html?id=' + row.id
            + '"><img src="';

    htmlString += row.volumeInfo.imageLinks.thumbnail + '"';
    htmlString += 'class="ui-li-has-thumb"/><h3>';
    if ($.isArray(row.volumeInfo.authors) && row.volumeInfo.authors.length > 0) {
        // code for what to do with json here
        htmlString += row.volumeInfo.title + '</h3><p>'
                + row.volumeInfo.authors[0] + '</p></a></li>';
    } else {
        htmlString += row.volumeInfo.title + '</h3><p>' + "Author Undifined"
                + '</p></a></li>';
    }

    console.log(htmlString);

    // append new html to the list
    $('#book_list').append(htmlString);
});

$('#book_list').listview('refresh');
// refresh the list-view so new elements are added to the DOM

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