我如何 select 中的 TypeScript / JavaScript 字符串文字类型针对单个按位和的特定值？

Question

How do I select specific values from TypeScript / JavaScript String Literal Types against a single bitwise sum? As a helper there can be a map of the Literal Types with bitwise keys: 1, 2, 4, 8, ... I am not sure how to put the result / return value together so it returns the result compatible with the given type.

Variant 1:

  const result: "Aaa" | "Bbb" | "Ccc" | "Ddd" = selectByBitwiseSum1(5);

  // THE EXPECTED RESULT:
  result = "Aaa" | "Ccc";


  export function selectByBitwiseSum1(bitwiseSum: number): "Aaa" | "Bbb" | "Ccc" | "Ddd" {

    var result;

    var optMap = [ {key: 1, val: "Aaa"},
                   {key: 2, val: "Bbb"},
                   {key: 4, val: "Ccc"},
                   {key: 8, val: "Ddd"}  ];

    // THE DESIRED CONVERSION PLEASE  TO RETURN GIVEN TYPE (NOT STRING ARRAY)
    result = ???

                  // THE EXPECTED RESULT:
    //result = "Aaa" | "Ccc";

    return result;
    
  }

Variant 2 - array type:

  const result: ("Aaa" | "Bbb" | "Ccc" | "Ddd")[] = selectByBitwiseSum2(5);

  result = ("Aaa" | "Ccc")[];


  export function selectByBitwiseSum2(bitwiseSum: number): ("Aaa" | "Bbb" | "Ccc" | "Ddd")[] {

    var result;

    var optMap = [ {key: 1, val: "Aaa"},
                   {key: 2, val: "Bbb"},
                   {key: 4, val: "Ccc"},
                   {key: 8, val: "Ddd"}  ];


    // THE DESIRED CONVERSION PLEASE  TO RETURN GIVEN TYPE (NOT STRING ARRAY)
    result = ???
                  // THE EXPECTED RESULT:
    //result = ("Aaa" | "Ccc")[];

    return result;
    
  }

Answer 1

You can do the whole thing with this one-liner

 const arr="AAA,BBB,CCC,DDD,EEE,FFF".split(","); console.log((5).toString(2).split("").reverse().reduce((a,c,i)=>(.+c||a,push(arr[i]),a).[]).join(" | "))

.+c||a,push(are[i],a probably deserves a little explanation: c is a single digit ("0" or "1") of the binary representation of the number 5 , starting with the "least significant bit" (since I .reverse() d the array). The + in front of it converts the string into an integer and the negation operator ! turns it into true or false . The part after the following || operator will only be executed, if the first expression was false .