Unable to delete a JSON object containing an empty value

Question

Unable to delete a JSON object containing an empty value

Currently, I am dealing with data retrieved from an API that includes both title and author attributes (referred to as title_1 and title_2 in this case). To streamline the process of saving data to my database, I have set a condition where an item is deemed invalid if both title_1 and title_2 are empty.

While this method appears to work correctly for the author attribute, I keep encountering a scenario where an item is still saved even when title_1 is null and title_2 is "". I suspect there might be an issue within how the values are being parsed.

Here is the JSON snippet of the problematic item:

"title_1": null,
"title_2": "",

Upon fetching and parsing the data, the following code is used:

request.get(apiUrl, function(error, response, body) {
      if(!error && response.statusCode == 200) {
        var data = JSON.parse(body);
        callback(error, data.items);
      }
    });

Subsequently, the function removeInvalidItems(data); is called which carries out the filtering process:

function removeInvalidItems(data) {
  for (var i = 0; i < data.length; i++) {
    if ( !isValid(data[i].title) && !isValid(data[i].title_2) ) {
      data.splice(i, 1);
    }
    if ( !isValid(data[i].author) && !isValid(data[i].author_2) ) {
      data.splice(i, 1);
    }
  }
  return data;
};

The validity check is performed using the following logic:

function isValid(attr) {
  if (attr === null || attr === '') {
    return false;
  } else return true;
};

If anyone has insights on why this particular item continues to pass through the isValid() function as valid, please share your thoughts.

javascript json parsing

Answer 1

Answer №1

It seems that the issue arises when you use splice(i, 1) to remove elements from an array, as this operation shifts the "current index" to the next element in the array. Take a look at the following example where we attempt to remove odd items from an array:

var arr = [1, 2, 3, 4, 5, 6];

for(var i = 0; i < arr.length; i++) {
  if(i % 2 == 1)
    arr.splice(i, 1);
}

alert(arr);

To resolve this issue, adjust the current index by reducing i by 1 after performing a splice operation:

function removeInvalidItems(data) {
  for (var i = 0; i < data.length; i++) {
    if ( !isValid(data[i].title) && !isValid(data[i].title_2) ) {
      data.splice(i--, 1);
    }
    if ( !isValid(data[i].author) && !isValid(data[i].author_2) ) {
      data.splice(i--, 1);
    }
  }
  return data;
};

Additionally, you can simplify your isValid function with the following implementation:

function isValid(attr) {
  return attr instanceof String && attr.length > 0;
};

Answer 2

It seems that the issue arises when you use splice(i, 1) to remove elements from an array, as this operation shifts the "current index" to the next element in the array. Take a look at the following example where we attempt to remove odd items from an array:

var arr = [1, 2, 3, 4, 5, 6];

for(var i = 0; i < arr.length; i++) {
  if(i % 2 == 1)
    arr.splice(i, 1);
}

alert(arr);

To resolve this issue, adjust the current index by reducing i by 1 after performing a splice operation:

function removeInvalidItems(data) {
  for (var i = 0; i < data.length; i++) {
    if ( !isValid(data[i].title) && !isValid(data[i].title_2) ) {
      data.splice(i--, 1);
    }
    if ( !isValid(data[i].author) && !isValid(data[i].author_2) ) {
      data.splice(i--, 1);
    }
  }
  return data;
};

Additionally, you can simplify your isValid function with the following implementation:

function isValid(attr) {
  return attr instanceof String && attr.length > 0;
};

Answer 3

Answer №2

When consecutive invalid items are encountered in your loop, the second one is not checked because you are altering the array while iterating over it.

To understand this behavior better, try running the following code snippet in a console:

data = [10, 1, 2, 3, 20, 30];
for (var i = 0; i < data.length; i++) {
    console.log('checking i=', i, 'data[i]=', data[i]);
    if (data[i] < 5) {
        console.log('removing i=', i, 'data[i]=', data[i]);
        data.splice(i, 1);
    }
}
console.log('Remaining data:', data);

Instead of directly modifying the array as shown above, a more reliable approach would be to use the filter method.

Answer 4

When consecutive invalid items are encountered in your loop, the second one is not checked because you are altering the array while iterating over it.

To understand this behavior better, try running the following code snippet in a console:

data = [10, 1, 2, 3, 20, 30];
for (var i = 0; i < data.length; i++) {
    console.log('checking i=', i, 'data[i]=', data[i]);
    if (data[i] < 5) {
        console.log('removing i=', i, 'data[i]=', data[i]);
        data.splice(i, 1);
    }
}
console.log('Remaining data:', data);

Instead of directly modifying the array as shown above, a more reliable approach would be to use the filter method.

Unable to delete a JSON object containing an empty value

Answer №1

Answer №2

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