Encountered an issue with undefined property when attempting to add a second value to an array of

Question

Encountered an issue with undefined property when attempting to add a second value to an array of

I have been working on the following javascript code:

 var res = [{}];
    for (var idx = 0; idx < json.length; idx++) {
        // if the environment is already entered in the result
        if (res[idx].env) {
            sails.log.debug('Environment is in result');
            // if the current inspected value has been deployed later than the stored one
            if (res[idx].updatedAt < json[idx].updatedAt) {
                sails.log.debug('Updating the value in the result');
                //res[json[idx].lifeCycle] = JSON.parse('{"'+json[idx].version+'":"'+json[idx].updatedAt+'"}');
                res.env = json[idx].lifeCycle;
                res.ver = json[idx].version;
                res.updatedAt = json[idx].updatedAt;
            }
        } else {
            // it is the first time we are adding to the result the component version (for the given environment)
            if (json[idx].lifeCycle) {
                //add the value in result
                res[idx].env = json[idx].lifeCycle || '';
                res[idx].ver = json[idx].version || '';
                res[idx].updatedAt = json[idx].updatedAt || '';
            }
            else {
                sails.log.debug('Lifecycle is null or empty');
            }
        }
    }
    return res;

This particular code snippet deals with handling a JSON object that contains multiple elements and values. Upon reaching the final block of code which reads:

if (json[idx].lifeCycle) {
                //add the value in result
                res[idx].env = json[idx].lifeCycle || '';
                res[idx].ver = json[idx].version || '';
                res[idx].updatedAt = json[idx].updatedAt || '';
            }

During this iteration, IDX is set to 1, marking the second cycle through the for loop.

However, when attempting to insert the second value into "res", I encounter the error message:

TypeError: Cannot read property 'env' of undefined

It seems as though after the initial pass through the for loop, the variable 'res' no longer exists. Can someone provide guidance on why this issue is occurring?

Thank you in advance!

javascript json

Answer 1

Answer №1

Upon examining your res array, it becomes evident that it contains only one element - an empty object. This signifies that :

res[0] // -> {}

and

res[1] // -> undefined

Straightforward solution (minimal changes to code)

The simplest approach is to generate a new object when accessing the res[idx] element within the array.

Your revised code snippet would resemble this

if (json[idx].lifeCycle) {
  res[idx] = res[idx] || {}; // if index `idx` is not defined, initialize it asan empty object
  res[idx].env = json[idx].lifeCycle || '';
  res[idx].ver = json[idx].version || '';
  res[idx].updatedAt = json[idx].updatedAt || '';
}

Improved solution

An alternative is to simplify the code by creating a fresh object in each loop iteration and pushing it into the res array. In doing so, you should also initialize the res array as an empty array var res = []:

if (json[idx].lifeCycle) {
  res.push({
    env: json[idx].lifeCycle || '',
    ver: json[idx].version || '',
    updatedAt: json[idx].updatedAt || ''
  })
}

This method eliminates the need to handle special cases regarding the existence of elements in the array, treating every loop uniformly

Optimal solution (Personal preference): embracing functional programming

In case you are unfamiliar with array functions like Array.prototype.map, they enable the application of a function to each element of an array, transforming them into altered elements and constructing a new array comprising these transformed entities.

Below is how the code appears incorporating the marvelous map method:

var res = json
    .map(function (element) {
      return {
        env: json[idx].lifeCycle || '',
        ver: json[idx].version || '',
        updatedAt: json[idx].updatedAt || ''
      }
    });

If my understanding is correct, res will contain identical values compared to your current code implementation.

I have omitted the initial condition if (res[idx].env) which I believe is unlikely to be true since res[idx] can solely be either undefined or an empty object (although my assumption may be flawed).

Should you find this solution appealing, make sure to explore the documentation on map, filter, and reduce on MDN :) https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/map

Answer 2

Upon examining your res array, it becomes evident that it contains only one element - an empty object. This signifies that :

res[0] // -> {}

and

res[1] // -> undefined

Straightforward solution (minimal changes to code)

The simplest approach is to generate a new object when accessing the res[idx] element within the array.

Your revised code snippet would resemble this

if (json[idx].lifeCycle) {
  res[idx] = res[idx] || {}; // if index `idx` is not defined, initialize it asan empty object
  res[idx].env = json[idx].lifeCycle || '';
  res[idx].ver = json[idx].version || '';
  res[idx].updatedAt = json[idx].updatedAt || '';
}

Improved solution

An alternative is to simplify the code by creating a fresh object in each loop iteration and pushing it into the res array. In doing so, you should also initialize the res array as an empty array var res = []:

if (json[idx].lifeCycle) {
  res.push({
    env: json[idx].lifeCycle || '',
    ver: json[idx].version || '',
    updatedAt: json[idx].updatedAt || ''
  })
}

This method eliminates the need to handle special cases regarding the existence of elements in the array, treating every loop uniformly

Optimal solution (Personal preference): embracing functional programming

In case you are unfamiliar with array functions like Array.prototype.map, they enable the application of a function to each element of an array, transforming them into altered elements and constructing a new array comprising these transformed entities.

Below is how the code appears incorporating the marvelous map method:

var res = json
    .map(function (element) {
      return {
        env: json[idx].lifeCycle || '',
        ver: json[idx].version || '',
        updatedAt: json[idx].updatedAt || ''
      }
    });

If my understanding is correct, res will contain identical values compared to your current code implementation.

I have omitted the initial condition if (res[idx].env) which I believe is unlikely to be true since res[idx] can solely be either undefined or an empty object (although my assumption may be flawed).

Should you find this solution appealing, make sure to explore the documentation on map, filter, and reduce on MDN :) https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/map

Encountered an issue with undefined property when attempting to add a second value to an array of

Answer №1

Straightforward solution (minimal changes to code)

Improved solution

Optimal solution (Personal preference): embracing functional programming

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