javascript 如何检查 JSON 数据中是否存在值/属性
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How to check if a value/property exist in JSON data
提问by Lali Pali
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.
我正在使用 Google Books API 来接收图书列表，但有时某些图书条目没有某些键/属性，例如Authors或没有Thumbnail。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。
Example Json data example from a book search containing the keywork Java
来自包含关键字 Java 的书籍搜索的示例Json 数据示例
Full link
完整链接
https://www.googleapis.com/books/v1/volumes?q=java&callback=jQuery191020691258599981666_1377508821982&_=1377508821983
E.g., when Authorsis missing
例如，当Authors丢失时
TypeError: row.volumeInfo.authors is undefined
I tryied two solutions suggested
我尝试了两个建议的解决方案
if ( typeof (authors) != "undefined"){}
and
和
if('authors' in booksObject) {}
but non of them seems to work, since they never enter the loops even when this proerty exists.
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。
This is where I call
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
};
采纳答案by Arun P Johny
You can check $.isArray(row.volumeInfo.authors) && row.volumeInfo.authors.length > 0
你可以检查 $.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
回答by Sushrut
Try this :
试试这个 ：
if(booksObject.image) {
//do stuff with it
} else if( booksObject.author ) {
//do stuff with author
}
回答by e.w. parris
Here's a really simple way to check if any key or value exists in your JSON.
这是一种非常简单的方法来检查您的 JSON 中是否存在任何键或值。
var jsonString = JSON.stringify(yourJSON);
if (jsonString .indexOf("yourKeyOrValue") > -1){
console.log("your key or value exists!");
}
It's quick, simple, easy.
它快速、简单、容易。
