javascript - How to update Map object property values? - Stack Overflow

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I am trying to find a best way to update object property values which are on Map, however it seems like there isn't a specific function for this.

Example:

const map = new Map();
map.set('kfwwwdvh', { first: 1, second: 2});

Now I would like to update 'first' property value, but if I do this

map.set('kfwwwdvh', { first: 'updated value'});

It will output this:

{ first: 'updated value'}

My question is how do I update object property values without overwriting other values the object has (in this example 'second' property and value), what is the best way to achieve this?

I am trying to find a best way to update object property values which are on Map, however it seems like there isn't a specific function for this.

Example:

const map = new Map();
map.set('kfwwwdvh', { first: 1, second: 2});

Now I would like to update 'first' property value, but if I do this

map.set('kfwwwdvh', { first: 'updated value'});

It will output this:

{ first: 'updated value'}

My question is how do I update object property values without overwriting other values the object has (in this example 'second' property and value), what is the best way to achieve this?

• javascript

Share Improve this question Follow edited Oct 9, 2020 at 10:34 Kristjan Ranna asked Oct 9, 2020 at 10:21 Kristjan RannaKristjan Ranna 5311 silver badge55 bronze badges

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2 Answers 2

Sorted by: Reset to default 4

You can update the property by first retrieving the object from the map using .get(), and then update the property of the returned object reference like so:

const map = new Map();
map.set('kfwwwdvh', { first: 1, second: 2});

map.get('kfwwwdvh').first = 'updated value';
console.log(map.get('kfwwwdvh'));

This will update the actual object in place, meaning if any references of it reside anywhere they will also be updated. This may be a good or bad thing depending on what behaviour you're after. For example:

const map = new Map();
map.set('kfwwwdvh', { first: 1, second: 2});
const obj = map.get('kfwwwdvh');

map.get('kfwwwdvh').first = 'updated value';
console.log(map.get('kfwwwdvh'), obj); // both updated

The only way is to set the value on the map key by overriding that first value as follows.

map.set('kfwwwdvh', {
  ...map.get('kfwwwdvh'),
  first: 'updated value'
});

const map = new Map();

map.set('kfwwwdvh', { first: 1, second: 2});
console.log(map.get('kfwwwdvh'));

map.set('kfwwwdvh', {
  ...map.get('kfwwwdvh'),
  first: 'updated value'
});
console.log(map.get('kfwwwdvh'));

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