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I want to use my variable children for different cases:

var children = [];

if (folderPath == '/') {
      var children = rootFolder;
} else {
      var children = folder.childs;
}

But I get the error message:

variable 'children' must be of type 'any[]' but here has type 'Folder[]'

What does this mean?

about 4 years ago · Santiago Trujillo

Answer question

Accepted Answer · 2022-07-21T15:55:57.665Z

In general, if "using a variable for different cases" involves using them for different types, then you're Doing Something Wrong.

Assuming rootFolder is of type Folder, and folder.childs is Folder[], your code looks like it could be something like

const children: Folder[] = (folderPath === '/' ? [rootFolder] : folder.childs);

and in fact you should be able to just do

const children = (folderPath === '/' ? [rootFolder] : folder.childs);

too and let inference handle things.

If you want to use if, then

let children: Folder[];

if (folderPath === '/') {
   children = [rootFolder];
} else {
   children = folder.childs;
}

should be fine; TypeScript will notice the variable is always definitely set after that if, even if it has no initial value.