数组中的值未定义 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?

Answer 1

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> )