The array is showing as empty with a length of 0, despite the fact that the debug console displays items

Question

The array is showing as empty with a length of 0, despite the fact that the debug console displays items

Something unusual is happening with my code. Most answers I've seen online talk about waiting for data, but that's not the issue here; the JSON source is within the HTML itself.

An array of items mysteriously has a length of zero, causing the forEach loop to fail. Here's the snippet with the console output:

// Container class

public inspectionTypes: SelectionOption[] = [];

// further down

public initializeInspectionTypes(types: any[]) {

    if (types) {

        types.forEach(t => {

            this.inspectionTypes.push(t);
        });
    }
}

// Some other class

console.debug('Type:', typeof container.inspectionTypes);
console.debug('Is Array:', Array.isArray(container.inspectionTypes));
console.debug('Length:', container.inspectionTypes.length);
console.debug(container.inspectionTypes);

container.inspectionTypes.forEach(option => {

    console.debug(option);

    // this.inspectionTypes().push(option);

});

Even though the console shows the array as populated, its length remains 0, leading to confusion. Check out the screenshot for more clarity:

https://i.sstatic.net/vTlax8co.png

To rule out any misunderstandings, here's another screenshot showing the logging of inspectionTypes first in case you suspect it's being emptied somewhere:

https://i.sstatic.net/JpPgS6W2.png

typescript

Answer 1

Answer №1

When you look at the array values displayed, they represent the current state of the array in memory. For example, consider this simplified scenario...

let myArray = ['apple', 'orange', 'banana'];

console.log(myArray.length); // 3
console.log(myArray);

myArray.pop()
myArray.pop()

console.log(myArray.length); // 1
console.log(myArray);

myArray.push('new fruit')

The key point here is that the array reference remains constant. Thus, when we use console.log, we see the correct values at that moment. However, the browser console displays the live reference to the array.

If you were to run the above scenario in the browser and inspect the values, it would appear as follows...

Observe how the initial log shows ['apple', 'orange', 'banana'] while the actual array contains ['apple', 'new fruit'], reflecting the real-time changes.

Alternatively, if you were to modify the array reference by reassigning the variable myArray, like so:

let myArray = ['apple', 'orange', 'banana'];

console.log(myArray.length); // 3
console.log(myArray);

myArray = ['apple']

console.log(myArray.length); // 1
console.log(myArray);

myArray.push('new fruit')

The initial console.log still displays the initial values because it points to the original array ['apple', 'orange', 'banana']. However, the subsequent log presents the modified array (i.e., ['apple']), which was not reassigned; only operations such as pop and push were performed on it.

In essence, this distinction should not impact your code's functionality.

Answer 2

When you look at the array values displayed, they represent the current state of the array in memory. For example, consider this simplified scenario...

let myArray = ['apple', 'orange', 'banana'];

console.log(myArray.length); // 3
console.log(myArray);

myArray.pop()
myArray.pop()

console.log(myArray.length); // 1
console.log(myArray);

myArray.push('new fruit')

The key point here is that the array reference remains constant. Thus, when we use console.log, we see the correct values at that moment. However, the browser console displays the live reference to the array.

If you were to run the above scenario in the browser and inspect the values, it would appear as follows...

Observe how the initial log shows ['apple', 'orange', 'banana'] while the actual array contains ['apple', 'new fruit'], reflecting the real-time changes.

Alternatively, if you were to modify the array reference by reassigning the variable myArray, like so:

let myArray = ['apple', 'orange', 'banana'];

console.log(myArray.length); // 3
console.log(myArray);

myArray = ['apple']

console.log(myArray.length); // 1
console.log(myArray);

myArray.push('new fruit')

The initial console.log still displays the initial values because it points to the original array ['apple', 'orange', 'banana']. However, the subsequent log presents the modified array (i.e., ['apple']), which was not reassigned; only operations such as pop and push were performed on it.

In essence, this distinction should not impact your code's functionality.

The array is showing as empty with a length of 0, despite the fact that the debug console displays items

Answer №1

Similar questions

Issue: ASSERTION ERROR: token must be declared [Expecting => null is not undefined <=Actual]

Is there a way to extract information from an HttpClient Rest Api through interpolation?

Comparing two inherited classes in Typescript: A step-by-step guide

I'm having trouble establishing a connection with the Appwrite platform

Add the slide number and total count in between the navigation arrows of the owl carousel

Having difficulty passing a function as a parameter from a NextJS component

Encountering the error message 'array expected for services config' within my GitLab CI/CD pipeline

Why aren't the child elements in my React / Framer Motion animation staggered as expected?

How can I create a computed field in TypeORM by deriving its value from other fields within the same Entity?

Guide to implementing scheduled tasks in a Node.js API using Express

What is the best way to transform a standard array into a record without losing the specific data types in each position?

Angular2 encounters an error when attempting to build, displaying the message: "Unable to proceed operation, directory creation not allowed, mkdir 'dir

What is the best way to integrate Emotion styled components with TypeScript in a React project?

Displaying HTML content using Typescript

Ionic 3 Storage Timing Explained

Implementing serialization and deserialization functionality in Typescript for classes containing nested maps

Transforming API data into a particular type using Typescript

"The list of table rows in a React application using Typescript is not rendering properly

Using Html to differentiate input based on type

Inquiry regarding the implementation of DTO within a service layer parameter