How to make iterator usable inside async callback function All Versions

Examples

• 0

  Correct Writing
  0

  var pipeline = {};
  // (...) adding things in pipeline
  
  var processOneFile = function(key) {    
    fs.stat(pipeline[key].path, function(err, stats) {
      if (err) {
        // clear that one
        delete pipeline[key];
        return;
      }
      // (...)
      pipeline[key].count++;
    });
  };
      
  // verify it is not growing
  for(var key in pipeline) {
    processOneFileInPipeline(key);
  }
  

  By creating a new function, we are scoping key inside a function so all callback have their own key instance.

  created Dec 7 '16 at 23:59

  
  discuss
• 0

  Erroneous code, can you spot why this usage of key will lead to bugs?
  0

  var pipeline = {};
  // (...) adding things in pipeline
  
  for(var key in pipeline) {
    fs.stat(pipeline[key].path, function(err, stats) {
      if (err) {
        // clear that one
        delete pipeline[key];
        return;
      }
      // (...)
      pipeline[key].count++;
    });
  } 
  

  The problem is that there is only one instance of var key. All callbacks will share the same key instance. At the time the callback will fire, the key will most likely have been incremented and not pointing to the element we are receiving the stats for.

  created Dec 7 '16 at 23:59

  
  discuss