I want to get the first number value out of values with number or undefined range.
Obviously this fails for 0 which is falsy. What is the logical expression to return this?
type Nomber = number | undefined
function a_or_b_or_c_number_value_including_zero(a: Nomber, b: Nomber, c: Nomber) {
return (a || b || c)
}
const test = (a: Nomber, b: Nomber, c: Nomber, expected: any) => {
let got = a_or_b_or_c_number_value_including_zero(a, b, c)
if (got !== expected) {
console.log([a, b, c], 'fail', got, expected)
}
}
test(1, 2, 3, 1)
test(undefined, 1, 2, 1)
test(0, 1, 2, 0)
test(undefined, 0, 2, 0)
You can use the nullish coalescing operator to check it.
According to MDN:
The nullish coalescing operator (
??) is a logical operator that returns its right-hand side operand when its left-hand side operand isnullorundefined, and otherwise returns its left-hand side operand.
This can be used in your code like below.
function a_or_b_or_c_number_value_including_zero(a: Nomber, b: Nomber, c: Nomber) {
return (a ?? b ?? c); // Modified
}
This will make the code work the way you want, which will not make 0 equal to false.
This is how the code works.
| Code | Description |
|---|---|
a ?? |
If a isn't null or undefined, use a. |
b ?? c |
If b is null or undefined, use c, else, use b. |
In conclusion, the nullish coalescing operator is a useful feature to not make 0 and "" equal to false (while || evaluates those values to false).
You can use the the Nullish coalescing operator (??) to workaround the 0 failing for being falsy.