Property does not exist error

[agile lynx]

So I have a check like this

var invalid = check(username, address);
if (invalid) {
        errorText.innerHTML = invalid.message;
        errorText.style.display = "block";
        return;
    }

and my function

function check(username: string, address: string): Error | boolean{
if (!username || typeof username !== "string" || username === "") {
        const err = new Error("Please provide a username.");
        return err;
}
return false

as you can see my check function returns an error or false if no error is present, in the first code block I check if error is present and then show message, but ts gives me this error "Property 'message' does not exist on type 'true | Error'.
Property 'message' does not exist on type 'true'

[severe mural]

multiple things

typeof username !== "string" is kinda useless

you told TS your function only accepts strings, so username won't ever be anything other that a string

!username and username === "" are redundant

an empty string ("") is falsy

so you don't need to check both, one check is enough

also, don't return Error

if your function didn't get the right arguments, throw an error instead

that you will catch where you call that check function

your check function doesn't need to return anything, its return type can thus be void

this leaves us with something like this

[half harbor]

Ascor8522#7606

Playground Link

Preview:```ts
function check(
username: string,
address: string
): void {
if (!username) new Error("Username cannot be empty.")
}

declare const errorText: HTMLDivElement
declare const username: string
declare const address: string

function foo() {
try {
check(username, add
...```

You can choose specific lines to embed by selecting them before copying the link.

[severe mural]

@agile lynx

[agile lynx]

Ok thank you so much for the detailed explanation and tips, will change my code accordingly.