Question

使用tumblr API构建项目时，

var latest = [];
client.posts('XXXXXX', function (err, blog) {
    for (var i = 0; i <

    blog.posts.length; i++) {
        var post = blog.posts[i];
        // this condition is used to identify if any blog post is dated no later than 7 days. 
        if ((new Date().valueOf() - Date.parse(post.date)) /(1000*60*60*24) <= 7){   latest.push(post); 
/ / console.log(post);
        }
    };
});

console.log(latest)

latest是一个变量存储满足条件的任何博客帖子对象。取消注释console.log（post）时，命令行会打印post对象，如下所示：

{ blog_name: '......',
  id: ......,
  post_url: '......',
  slug: '......',
  type: 'text',
  date: '2015-07-20 16:42:30 GMT',
  timestamp: ....,
  state: 'published',
  format: 'html',
  reblog_key: '.....',
  tags: [],
  short_url: '.......',
  recommended_source: null,
  followed: false,
  highlighted: [],
  liked: false,
  note_count: 0,
  title: '.....',
  body:.......}

但是，对于console.log（最新），命令行打印[]。为什么最新在这里返回一个空数组？

Answer 1

正如评论中所指出的那样，client.posts()是一种异步方法，所以它不像你期望的那样按顺序工作。

var latest = [];
client.posts('XXXXXX', function (err, blog) {
    // This is not reached until AFTER you hear back from the API
    // and latest has already been logged.
});

console.log(latest)

如果您想等到打印直到您从API中回复，那么您将需要使用一些异步编程方法（如promises）或在client.posts回调中添加您想要的功能

这将正确打印：

var latest = [];
client.posts('XXXXXX', function (err, blog) {
    for (var i = 0; i < blog.posts.length; i++) {
        var post = blog.posts[i];
        if ((new Date().valueOf() - Date.parse(post.date)) /(1000*60*60*24) <= 7){
            latest.push(post);
        }
    }
    console.log(latest); // Prints when for loop completes
});

当分配了值时，数组对象返回空 - Javascript

1 个答案: