需要 Javascript 帮助 - 哪个变量返回空？

Question

我想知道如何为下面提到的代码添加错误检查...我的意思是如何检查此代码是否返回空值？？如果这返回为空，那么我会给出一条消息“未找到”..我该怎么做？？

google.load('search', '1');

var blogSearch;

function searchComplete() {

  // Check that we got results
  document.getElementById('content').innerHTML = '';
  if (blogSearch.results && blogSearch.results.length > 0) {
    for (var i = 0; i < blogSearch.results.length; i++) {

      // Create HTML elements for search results
      var p = document.createElement('p');
      var a = document.createElement('a');
      a.href = blogSearch.results[i].postUrl;
      a.innerHTML = blogSearch.results[i].title;

      // Append search results to the HTML nodes
      p.appendChild(a);
      document.body.appendChild(p);
    }
  }
}

function onLoad() {

  // Create a BlogSearch instance.
  blogSearch = new google.search.BlogSearch();

  // Set searchComplete as the callback function when a search is complete.  The
  // blogSearch object will have results in it.
  blogSearch.setSearchCompleteCallback(this, searchComplete, null);

  // Set a site restriction
  blogSearch.setSiteRestriction('blogspot.com');

  // Execute search query
  blogSearch.execute('1974 Chevrolet Caprice');

  // Include the required Google branding
  google.search.Search.getBranding('branding');
}

// Set a callback to call your code when the page loads
google.setOnLoadCallback(onLoad);

Answer 1

您已经检查过搜索结果是否不为空:

 if (blogSearch.results && blogSearch.results.length > 0) {

您只需在 if block 的右括号之后添加一个 else block :

function searchComplete() {

  // Check that we got results
  document.getElementById('content').innerHTML = '';
  if (blogSearch.results && blogSearch.results.length > 0) {
    for (var i = 0; i < blogSearch.results.length; i++) {

      // Create HTML elements for search results
      var p = document.createElement('p');
      var a = document.createElement('a');
      a.href = blogSearch.results[i].postUrl;
      a.innerHTML = blogSearch.results[i].title;

      // Append search results to the HTML nodes
      p.appendChild(a);
      document.body.appendChild(p);
    }
  }
  else {  // <-- HERE!
      document.getElementById("content").innerHTML = "Not found.";
  }
}