ES6 Map key to be either string or number

Question

I have a ES6 Map , where keys are number. Some time the key is number and some time the key is string which represents a number. The map will never have duplicate key at runtime for me. Example I will never have key "1" and 1 .

While retrieving from map I need a simple one liner code which will negate whether if the key is a string or a number.

var map = new Map();
undefined
map.set('1', 'string one');
map.set(2, 'number tow')
Map(2) {"1" => "string one", 2 => "number tow"}
map.get(1)
undefined
map.get('1')
"string one"

You'd better rethink your appoach and stick with either numbers or strings. — Yury Tarabanko, Nov 14 '17 at 12:14
I agree with @NinaScholz there's no point in using a `Map` if you're never gonna have both `1` and `'1'` ... — Ante Jablan Adamović, Nov 14 '17 at 12:36

score 4 · Answer 1 · edited Nov 14 '17 at 23:51

4

You could use just an object with no prototypes. For the access the key is converted to string.

var map = Object.create(null);

map['1'] = 'string one';
map[2] = 'number two';

console.log(map[1]);   // 'string one'
console.log(map['1']); // 'string one'
console.log(map);

edited Nov 14 '17 at 23:51

Redu

19,106
4
44
59

answered Nov 14 '17 at 12:51

Nina Scholz

323,592
20
270
324

score 1 · Answer 2 · answered Nov 14 '17 at 12:23

1

I've created a function that gets the value from the given map. It works both ways, from string to int and from int to string.

var map = new Map();
map.set('1', 'string one');
map.set(2, 'number two');

function getFromMap(map, key){
  return map.get(key) || map.get(key.toString()) || map.get(parseInt(key));
}

console.log(getFromMap(map, 1));
console.log(getFromMap(map, '2'));

answered Nov 14 '17 at 12:23

Rick van Osta

953
9
19

This is adding a lot of complexity to each search of the map and can potentially slow down the script a lot since you are (in the worst case scenario) searching the map 3 times to find a single value ... – Ante Jablan Adamović Nov 14 '17 at 12:33
Correct, Nina Scholz's answer is a much better solution than this. – Rick van Osta Nov 14 '17 at 13:01

C'estLaVie · Answer 3 · 2017-11-14T14:25:19.770

For starters, I would recommend that you will sanitize your keys (e.g use only strings or only numbers) and by this you will make your life easier.

If you still insist on using both type of keys you could create a wrapper function like this :

function getFromMap(map, key){
    var stringKey = key.toString(); 
    var integerKey = parseInt(key);
    return map.get(stringKey) || map.get(integerKey);
}

As a side note : It seems that in your case you could easily use an ordinary object (Using brackets for object assignment will automatically convert the numbers to strings) :

var o = {};
o[1] = 'First value';
console.log(o[1] === o['1']); // true

For furthor reading about the advantages/disadvantages of using Map vs Objects you are invited to read the following SA question .

ES6 Map key to be either string or number

3 Answers3