They closed my question on SO because it's not reproducible, but that's exactly why I posted, because code isn't behaving as it should.

Anyway, I 'm receiving a JSON result from a web service. It looks something like this:

{ "data": [{ "id": "123ABC", "name" : "Test 1" }, { "id": "", "name" : "Test 2" }] }

I 'm looping through the data array and need to determine if an id exists or not:

for( const item of data ) {
    if( item.id !== null && item.id.trim().length > 0 ) {
        doSomething();
    } else {
        doSomethingElse();
    }
}

My problem is that doSomething() fires for the first item ("123ABC") but also fires for the second where the id is empty.

I've tried spitting out the values for the second item:

console.log("NULL ", item.id === null);
console.log("EMPTY ", item.id.trim().length === 0);

and results are

NULL  false
EMPTY  false

so I'm wondering if there's something strange about the id value.

I would like to create a type where it accepts all string except empty string. So buttonAriaLabel = "I am button" is acceptable, but if empty string is passed in buttonAriaLabel = " ", this will generate type error like "empty string is not assignable to type..." . I tried following technique (s: string): s is Excluse<typeof s, ' '> but it doesn't work at all. What are the techniques available to achieve this?

type NonEmptyString = {
  (s: string): s is Exclude<typeof s, ''>;
};
export interface IButton {
  // ... other properties
  buttonAriaLabel: NonEmptyString;
}

// Desired Result
const button: IButton = {
  // ... other properties
  buttonAriaLabel: 'Close', // Valid non-empty string
};
const invalidButton: IButton = {
  // ... other properties
  buttonAriaLabel: '' ", // TypeScript error: Type " " is not assignable to type 'NonEmptyString'.
};