Javascript Map Object with multiple keys to one value

Question

Is it possible to have multiple keys giving the same result in a JS Map, without having to write all of them ?

For example:

const mp = new Map<number, string>([
      [2 || 4, 'even'],
      [1 || 3, 'odd']
    ]);

This does not work but I am looking for something similar to avoid a switch case which is very verbose

This looks like an [XY-problem](https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem). What is the task you're doing with `switch`? (It probably is not an even-odd-check, which can be done easily without a map.) — Teemu, Jan 13 '22 at 11:12
Does this question help? https://stackoverflow.com/q/14743536/14032355 — ikhvjs, Jan 13 '22 at 11:13
JavaScript maps can't have duplicate keys, they must all be unique. See related: https://stackoverflow.com/questions/3996135/js-associative-object-with-duplicate-names — msalla, Jan 13 '22 at 11:16
@moritzsalla OP is talking about different keys with the same value, not for different values with the same key. — VLAZ, Jan 13 '22 at 11:21
I try to map a type with a string. Some types can get the same string — Auloma, Jan 13 '22 at 11:26

tao · Accepted Answer · 2022-01-13T11:57:17.750

4

You can write your own helper to transform a less verbose input into the one which new Map() expects:

const mapReducer = (arr, [keys, val]) => [
  ...arr,
  ...(Array.isArray(keys)
    ? [...keys.map(key => [key, val])]
    : [[keys, val]]
  )
];

const mp = new Map([
  [[2, 4], 'even'],
  [[1, 3], 'odd'],
  [0, 'meh...']
].reduce(mapReducer, []));

console.log([...mp.entries()])

edited Jan 13 '22 at 11:57

answered Jan 13 '22 at 11:27

tao

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2

Thanks, this is what I was loking for ! – Auloma Jan 13 '22 at 11:30

score 2 · Answer 2 · answered Jan 13 '22 at 11:07

Is it possible to have multiple keys giving the same result in a JS Map, without having to write all of them ?

No. A map is a 1:1 connection between a key and a value. If you want two different keys to have the same value, that means you need to create two entries in the map.

Javascript Map Object with multiple keys to one value

2 Answers2