const initialProgram = {
id: 0,
studentId : 0,
targets : []
}
const [program, setProgram] = useState(initialProgram);
In one of my functions I am updating the program as follows: setProgram({...program,studentId= selectedStudent?.id})
The type definition for selected Student is: selectedStudent: Student | undefined;
I need to make sure that selectedStudent remains unchanged.
How can I modify initialState to fix this error?
You have specified that the studentId property should hold a number.
selectedStudent?.id may be either a number or undefined.
Because undefined is not a number, an error occurs.
There are various ways to fix this error, but without more information, it is difficult to determine the best solution.
Check if the value is undefined and provide a default number
setProgram({
...program,
studentId: selectedStudent?.id ?? 0
});
Alternatively, use an explicit type that allows the property to be undefined
type Program = {
id: number;
studentId?: number;
targets: Something[]
}
const initialState: Program = {
id: 0,
studentId : 0,
targets : []
}
Handling the situation on the state side is crucial in determining the approach.
Based on the initialState, it can be deduced that studentId is expected to be a number. Since undefined is not a number, the error occurs when trying to assign selectedStudent?.id.
If you wish to default to 0 when selectedStudent is undefined, try the following alternative:
setProgram({...program, studentId= selectedStudent?.id ?? 0})
To define acceptable values for studentId in TypeScript, you can specify them as follows:
type StateType = {
id: number,
studentId?: number, // or number | undefined
targets: string[] // assuming string array
}
const initialState: StateType = {
id: 0,
studentId : 0,
targets : []
}
Alternatively,
const initialState = {
id: 0,
studentId : 0 as number | undefined,
targets: []
}
let initialData : any = {
userId: 1,
userName : 'John',
items : []
}
const [data, setData] = useState(initialData);
This code snippet is functioning correctly.
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