React Typescript: Cannot read properties of undefined

Question

The console is showing a new Object but I still get the error

const GetNo = (): string => {
        console.log(record);
        if (record.no !== "")
            return record.no;   //<-- Cannot read properties of undefined
        else
            return todos[todos.length - 1].no + 1;
    }

console:

EDIT: record is type of object (see picture above) and im creating it via Button onClick where i modify a state this.setState({ selectedRecord: new ToDoClass() . After that I redner the FC with the form.

EDIT 2: I tried the new Syntax:

const GetNo = (): string => {
        if (record == null) {
            console.log("1");
            return "2";
        }
        else if (record.no != null) {
            console.log("2");
            return record.no;
        }
        else {
            console.log("3");
            return todos[todos.length - 1].no + 1;
        }
    }

and when the record is: new ToDoClass() it return in the console a 2 but it should go inside the first statement?!

where is record defined in your code, e.g. const record = ....? — Jhecht
– Jhecht, Commented Jan 16, 2022 at 12:43

Thomas · Accepted Answer · 2022-01-15 20:58:23Z

3

Your object record is defined outside of the function and may not be initialized at the execution time of the function.

I recommend you to:

Pass the object as a parameter of the function
Check that record is defined

By the way if you're using Typescript and there is a possibility that the record is not defined when passed to the function, you should get a warning at the line where you call GetNo(record).

const GetNo = (record: Record): string => {
   if (record) {
     // ...
   }
}

I hope it will be helpful!

answered Jan 15, 2022 at 20:58

Thomas

313 bronze badges

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

1 Comment

Feisser Over a year ago

The check that the record is defined works but now it always return this if statement and dont go into the other statements

Feisser · Accepted Answer · 2022-01-16 12:41:15Z

0

I don't know why it behaves like this but I solved it with a Try-Catch statement.

const GetNo = (): string => {
   try {
      if (record.no !== "")
         return record.no;
      else
         return todos[todos.length - 1].no + 1;
   }
   catch {
      return "0";
   }
}

answered Jan 16, 2022 at 12:41

Feisser

191 gold badge3 silver badges19 bronze badges

Collectives™ on Stack Overflow

React Typescript: Cannot read properties of undefined

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related