Value in Array is undefined TypeScript

Question

I got an error in my foreach with an array:

function setRowData({ json }: NewType): void {
    // foreach key and value in json object
    // fill into an object
    // add object to array
    let tableRows: { id: string; key: string; de: string; it: string; }[] = [];
    Object.entries(json).forEach(([key, value]) => tableRows.push({
        id: key, key: key, de: value, it: (typeof value === 'string' ? value : "")
    }));
    setTableData(tableRows);
}

The error occurs on the line with the following content: id: key, key: key, de: value, it: (typeof value === 'string' ? value : "")

Does anyone know why the value variable called value inside my array is undefined?

In addition I post a photo of it and where the error occurs:

This one is the description of the foreach, why is the second type in the array undefined?

I suspect the issue is that the function param should be json instead of {json}. — Clarity
– Clarity, Commented Mar 27, 2022 at 8:19
@Clarity It should not be json because i need to get the correct values of my json and without the curly braces { } it won't be possible anymore... but of course this fixes the error but doesn't help anything more hahhaha — Noah
– Noah, Commented Mar 27, 2022 at 8:37

Sandro Maglione · Accepted Answer · 2022-03-27 08:21:12Z

2

When you use Object.entries() you extract an array of key-value tuples.

In this case the problem is that typescript cannot infer the type of values in the object, so it types it as unknown ([string, unknown][]).

The error is telling you that you cannot assign unknown to string.

In order to have it typed as string you must either specify it when using Object.entries():

const entries = Object.entries<string>(json);

Or you should specify in your NewType that json is an object with only string as values (using typescript's Record: Record<string, string>)

answered Mar 27, 2022 at 8:21

Sandro Maglione

3062 gold badges5 silver badges9 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Noah Over a year ago

if I use entries instead of Object.entries with your defined variable, then I can't specify the other stuff like key, value anymore... :/

Noah Over a year ago

Ah thanks Sandro, now it works if i say json is an object with only string as value. As you said: json: Record<string, string>

Collectives™ on Stack Overflow

Value in Array is undefined TypeScript

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related