如何检查 JSON 数据中是否存在值/属性 [英] How to check if a value/property exist in JSON data

问题描述

我使用 Google Books API 接收图书列表，但有时某些图书条目没有某些键/属性，例如 作者，或者没有缩略图.因此 JavaScript 说我试图访问的属性是未定义的，我的应用程序卡住了.

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.

示例 包含关键工作 Java

完整链接

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

例如，当作者丢失时

TypeError: row.volumeInfo.authors is undefined

我尝试了两种建议的解决方案

I tryied two solutions suggested

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

和

if('authors' in booksObject) {}

但它们似乎都不起作用，因为即使存在此属性，它们也永远不会进入循环.

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

这是我打电话的地方

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
};

推荐答案

您可以查看 $.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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