The attribute 'split' is not found on the never data type

Question

The attribute 'split' is not found on the never data type

I have a function that can update a variable called `result`. If `result` is not a string, the function will stop. However, if it is a string, I then apply the `split()` method to the `result` string.

This function always runs successfully without crashing. But TypeScript raises an error claiming:

"Property 'split' does not exist on type 'never'."

Take a look at the code snippet below:


function processData() {
    let data = userData[category] as { [key: string]: {} };

    ["employees", "tech"].forEach((key) => {
        if (!data[key]) return;
        return (data = data[key]);
    });

    if (typeof data !== "string") return null;
    
    // do more operations
}

How can this type issue be resolved?

javascript typescript

Answer 1

Answer №1

You have set the result variable to a null value explicitly:

let result = null;

As it stands, the condition:

if (typeof result !== "string")

will always be true. Therefore, the code that follows with return result... will never be executed.

If you adjust your function slightly to accept result as an argument, then the condition will work correctly and TypeScript will not raise any issues:

function foo(result: string | null) {  // accepts a possibly null result
    // perform operations
}

Answer 2

You have set the result variable to a null value explicitly:

let result = null;

As it stands, the condition:

if (typeof result !== "string")

will always be true. Therefore, the code that follows with return result... will never be executed.

If you adjust your function slightly to accept result as an argument, then the condition will work correctly and TypeScript will not raise any issues:

function foo(result: string | null) {  // accepts a possibly null result
    // perform operations
}

Answer 3

Answer №2

When looking at your code example, the result seems to be of type null and only null

If you want to allow it to accept both null and string, you must explicitly declare that

function foo(){
let result: string | null = null
// carry out some operations
if (typeof result !== "string") return null;
// do more operations
return result
        .split("__")
        .map((word:string) => word.toUpperCase())
        .join("")
    : result;
  }

In addition, depending on your TypeScript version, you can simplify these checks to make it a bit more succinct (using null coalescing and optional chaining)

function foo(){
  let result: string | undefined;

  // operate on result to potentially turn it into a string
  // continue with more operations

  return result
        ?.split("__")
        .map((word:string) => word.toUpperCase())
        .join("") ?? null
}

Answer 4

When looking at your code example, the result seems to be of type null and only null

If you want to allow it to accept both null and string, you must explicitly declare that

function foo(){
let result: string | null = null
// carry out some operations
if (typeof result !== "string") return null;
// do more operations
return result
        .split("__")
        .map((word:string) => word.toUpperCase())
        .join("")
    : result;
  }

In addition, depending on your TypeScript version, you can simplify these checks to make it a bit more succinct (using null coalescing and optional chaining)

function foo(){
  let result: string | undefined;

  // operate on result to potentially turn it into a string
  // continue with more operations

  return result
        ?.split("__")
        .map((word:string) => word.toUpperCase())
        .join("") ?? null
}

The attribute 'split' is not found on the never data type

Answer №1

Answer №2

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