CODEWITHSUNDEEP
javascriptarraysjsonnode.jsdictionary
chromedude
chromedude

Reputation: 4302

Why can you not return an object to Javascript's Array.map() and it map it properly?

I have two functions below (they are taken out of a larger script so assume everything is defined etc. self.sentenceObjs works great. It returns an object exactly like it's supposed to do. self.parseBodySections for some reason sets bodyJSON to an array of undefined even though self.sentenceObjs is returning perfect objects given the dom array of objects I want mapped. For some reason when I run dom.map(self.sentenceObjs) it returns undefined for each object. Any idea why this would be? Is there something with Array.map() that I missing?

  self.parseBodySections = function(dom, cb) {
    var bodyJSON = dom.map(self.sentenceObjs);
    console.log(bodyJSON); // prints: [ undefined, undefined, undefined, undefined, undefined ]

    return cb(null, bodyJSON);
  };

  self.sentenceObjs = function(section) {
    var paragraphToTextAndLinks = function(cb) {
      return self.paragraphToTextAndLinks(section.children, function(err, paragraphText, links) {
        if (err) {
          return cb(err);
        }

        return cb(null, paragraphText, links);
      });
    };

    return async.waterfall([
      paragraphToTextAndLinks,
      self.paragraphToSentences
    ],
    function(err, sentences, paragraphPlaintext) {
      var paragraph = {
        type: section.name,
        value: paragraphPlaintext,
        children: sentences
      };

      console.log(paragraph) // prints perfect object (too long to show here)

      return paragraph;
    });
  };

Upvotes: 1

Views: 537

Answers (1)

joewhite86
joewhite86

Reputation: 418

The problem is, that you return "paragraph" in the callback function of waterfall. So the function sentenceObjs returns nothing, or undefined.

You need to pass in a callback function to sentenceObjs and call async.map instead of Array.map:

self.parseBodySections = function(dom, cb) {
  async.map(dom, self.sentenceObjs, function(err, bodyJSON) {
    console.log(bodyJSON); // prints: [ undefined, undefined, undefined, undefined, undefined ]
    return cb(null, bodyJSON);
  });
};

self.sentenceObjs = function(section, cb) {
  var paragraphToTextAndLinks = function(cb) {
    return self.paragraphToTextAndLinks(section.children, function(err, paragraphText, links) {
      if (err) {
        return cb(err);
      }

      return cb(null, paragraphText, links);
    });
  };

  return async.waterfall([
    paragraphToTextAndLinks,
    self.paragraphToSentences
  ],
  function(err, sentences, paragraphPlaintext) {
    var paragraph = {
      type: section.name,
      value: paragraphPlaintext,
      children: sentences
    };

    console.log(paragraph); // prints perfect object (too long to show here)

    return cb(null, paragraph);
  });
};

Upvotes: 1

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