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)

CodePudding user response：

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 is null or undefined, and otherwise returns its left-hand side operand.

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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);
}

This will make the code work the way you want, which will not make 0 equal to false.

---

Basically, the code works like this:

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.

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In conclusion, the nullish coalescing operator is a useful feature to not make 0 and "" equal to false (while || evaluates those values to false).

CodePudding user response：

Use ?? instead of ||

function a_or_b_or_c_number_value_including_zero(a: Nomber, b: Nomber, c: Nomber) {
      return (a ?? b ?? c)
    }

CodePudding user response：

You can use the the Nullish coalescing operator (??) to workaround the 0 failing for being falsy.

CodePudding user response：

You can take advantage of rest parameters in order to write a function that accept any number of values and returns the first not undefined one:

type Nomber = number | undefined

function getFirstNumber(...values: Nomber[]) {
  for(let value of values){
    if (value !== undefined) return value;
  }
  return undefined;
}

You can see a Demo here

CodePudding user response：

Use rest parameter spread with Array.find, along with a nullish coalescing operator that will return false if no match is found.

const test = (...args) => args.find(v => v !== undefined) ?? false

console.log(test(1, 2, 3, 1))
console.log(test(undefined, 1, 2, 1))
console.log(test(0, 1, 2, 0))
console.log(test(undefined, 0, 2, 0))
console.log(test())