Here is the type structure I am working with:
type Child = {
foo: number | null
}
type Parent = {
child: Child | null
}
I am looking to create a type-guard function that takes in a Parent object as a parameter and checks if foo is a number. Something along the lines of:
const guard = (parent: Parent): parent?.child?.foo is number => {
return isNumber(parent?.child?.foo)
}
Is there a way for TypeScript to infer that parent.child is not null based on this type-guard function?
To explain it clearly, for example:
const guard = (parent: Parent): parent is {child: {foo: number}} => {
return isNumber(parent?.child?.foo);
};
You have the option to use intersection types, such as:
const guard = (parent: Parent): parent is Parent & {child: Child & {foo: number;};} => {
return isNumber(parent?.child?.foo);
};
(Instead of an inline intersection, you can always define a type for it.)
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