How to update the value of a javascript map with object key

Question

I have a map with an object as a key. For example: {date:"01/01/1990", idActiv:"4"}.

Then as a value, I have a string ("T" or "F") that represents True or False. My goal is to update that value, given a key.

var mapElem = new Map();

mapElem.set({date: "08/06/2020", idActiv: "1"}, "T");
mapElem.set({date: "18/06/2020", idActiv: "3"}, "T");

How I can update the map with object key {date: "08/06/2020", idActiv: "1"}?

If I do this:

mapElem.set({date: "08/06/2020", idActiv: "1"},"F");

I will have keyes repeated (Mozilla Firefox console):


mapElem.set({date: "08/06/2020", idActiv: "1"},"F");
Map(3)

size: 3

<entries>

0: Object { date: "08/06/2020", idActiv: "1" } → "T"

1: Object { date: "18/06/2020", idActiv: "3" } → "T"

2: Object { date: "08/06/2020", idActiv: "1" } → "F"

Does this answer your question? Using Array objects as key for ES6 Map — Ivar
– Ivar, Commented Jun 8, 2020 at 11:55
Also relevant: Map using tuples or objects. It mentions a possible solution being value objects. However, at the time that was planned for ES7 which went out years ago without this feature. The proposal is currently still at stage 1. — VLAZ
– VLAZ, Commented Jun 8, 2020 at 12:07

Józef Podlecki · Accepted Answer · 2020-06-08 11:56:03Z

0

You have to store objects as {date: "08/06/2020", idActiv: "1"} lone expression creates new instance somewhere

const obj1 = {date: "08/06/2020", idActiv: "1"};
const obj2 = {date: "18/06/2020", idActiv: "3"}
var mapElem = new Map();

mapElem.set(obj1, "T");
// mapElem.set(obj1.valueOf(), "T"); // equivalent
mapElem.set(obj2, "T");
// mapElem.set(obj2.valueOf(), "T"); // equivalent

mapElem.set(obj1, "F"); 
// mapElem.set(obj1.valueOf(), "F"); // equivalent

console.log([...mapElem.entries()]);

answered Jun 8, 2020 at 11:56

Józef Podlecki

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2 Comments

proera Over a year ago

Thats works. But I have $.each. So if I declare only one time the reference obj1, mapElem only will have one elem.

Józef Podlecki Over a year ago

Could you elaborate more on that?

Vimal Munjani · Accepted Answer · 2020-06-08 12:04:10Z

0

Since, Object is a reference type, 2 Objects even with the same properties (basically 2 identical objects) are different, as they are 2 different references. The following should work as they are using the same Object (same reference) as a key in the map

var mapElem = new Map();

const key1 = {date: "08/06/2020", idActiv: "1"};
const key2 = {date: "18/06/2020", idActiv: "3"};

mapElem.set(key1, "T");
mapElem.set(key2, "T");

The same refernce key can be used later to update the value in the Map -

mapElem.set(key1,"F");

Alternatively, if the use case do no necessarliy require the keys to be object, you can serialize the object JSON.stringify(object) before using it as the key

edited Jun 8, 2020 at 12:04

answered Jun 8, 2020 at 11:58

Vimal Munjani

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