A union type that includes integers and NaN as valid return values

Question

A union type that includes integers and NaN as valid return values

I have a function for comparison that has a union return type. It can return -1, 1, or 0. However, I need to handle a special case when at least one of the items being compared is not defined. While the compiler allows me to include null as a potential return value, it does not allow NaN (which could make sense in certain scenarios such as comparing numbers or dates).

The following code compiles successfully:

function myFunc(item1: MyType, item2: MyType): -1 | 0 | 1 | null {
   ...
}

However, when I try to add NaN as a possible return value like this:

function myFunc(item1: MyType, item2: MyType): -1 | 0 | 1 | NaN {
   ...
}

The compiler throws an error saying "Cannot find name NaN". Why is NaN not allowed? Is there any workaround to utilize NaN in this context?

typescript typescript2.0

Answer 1

Answer №1

NaN is actually not considered a type on its own; it is a const value belonging to the Number data type. Therefore, there is no direct way to designate something as being of the type NaN.

This discrepancy makes sense because number literal types are typically individual values such as -1, or a combination of specific numerical values like 1 | 0 | -1. In contrast, NaN cannot be compared directly with any other value, making it more akin to an unlimited set of possible values.

In light of this, using NaN to signify a certain outcome from your function may not be the best approach since testing for that result would require calling another function. It might be better to incorporate null, undefined, or even a predefined string into the return type instead.

It's important to remember that:

let foo = NaN;
switch(foo) {
    case 1: console.log('got 1'); break
    case NaN: console.log('got NaN'); break;
    default: console.log('other');
}

In this scenario, the output will be 'other'.

To address this issue, you could consider implementing the following solution:

function myFunc(item1: MyType, item2: MyType): -1 | 0 | 1 | 'not comparable' {
   ...
}

Subsequently, you can simply compare the returned result against 'not comparable'.

Answer 2

NaN is actually not considered a type on its own; it is a const value belonging to the Number data type. Therefore, there is no direct way to designate something as being of the type NaN.

This discrepancy makes sense because number literal types are typically individual values such as -1, or a combination of specific numerical values like 1 | 0 | -1. In contrast, NaN cannot be compared directly with any other value, making it more akin to an unlimited set of possible values.

In light of this, using NaN to signify a certain outcome from your function may not be the best approach since testing for that result would require calling another function. It might be better to incorporate null, undefined, or even a predefined string into the return type instead.

It's important to remember that:

let foo = NaN;
switch(foo) {
    case 1: console.log('got 1'); break
    case NaN: console.log('got NaN'); break;
    default: console.log('other');
}

In this scenario, the output will be 'other'.

To address this issue, you could consider implementing the following solution:

function myFunc(item1: MyType, item2: MyType): -1 | 0 | 1 | 'not comparable' {
   ...
}

Subsequently, you can simply compare the returned result against 'not comparable'.

Answer 3

Answer №2

Contrary to 1, the value of NaN cannot be assigned as a literal type (in other words, a type that only consists of that specific literal value).

const num1 = 1, num2 = NaN;
typeof num1; // 1
typeof num2; // number

Another option for the return type could be number, but this would permit additional return values such as -2. If the goal is to restrict the possibilities, then using null seems like a suitable choice.

Answer 4

Contrary to 1, the value of NaN cannot be assigned as a literal type (in other words, a type that only consists of that specific literal value).

const num1 = 1, num2 = NaN;
typeof num1; // 1
typeof num2; // number

Another option for the return type could be number, but this would permit additional return values such as -2. If the goal is to restrict the possibilities, then using null seems like a suitable choice.

A union type that includes integers and NaN as valid return values

Answer №1

Answer №2

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