Typescript Map with objects as keys

Question

I am trying to construct a map with object as keys and probably running to object instance related issues and would like to get some opinion here.

const x = new Map<{label: string, name: number}, string>();

x.set({label: 'x', name: 122}, 'r');
x.set({label: 'x', name: 122}, 'r1');

I can see that x is populated with two Object keys, while I am actually try to update the existing one and of course reads fail on this key as object.

My hunch is that keys are considered as two different object instances, is there a way for me to achieve this?

CertainPerformance · Accepted Answer · 2020-09-18 02:12:20Z

3

Separate objects are not ===, and a Map can hold multiple objects that are not === even if they contain the same keys and values.

You can search through the keys of the Map to find one with the same label and name, and set it if it exists:

const x = new Map();

x.set({label: 'x', name: 122}, 'r');

const newVal = 'r1';
const foundObj = [...x.keys()].find(
  key => key.label === 'x' && key.name === 122
);
if (foundObj) {
  x.set(foundObj, newVal);
} else {
  x.set({label: 'x', name: 122}, newVal);
}

console.log(x.get(foundObj));

That said, this is pretty verbose. Consider if you can use a plain object instead of a Map, whose keys are the stringified objects:

const x = {};

x[JSON.stringify({label: 'x', name: 122})] = 'r'

x[JSON.stringify({label: 'x', name: 122})] = 'r1'

console.log(Object.values(x));

edited Sep 18, 2020 at 2:12

answered Sep 18, 2020 at 2:09

CertainPerformance

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3 Comments

jfriend00 Over a year ago

FYI, there are issues with using JSON.stringify() in the way you show because: JSON.stringify({ label: 'x', name: 122 }) !== JSON.stringify({ name: 122, label: 'x' }) due to the ordering of the keys even though the keys are identical.

CertainPerformance Over a year ago

Yeah, if having differently ordered properties with the same values is a possibility (which is quite unusual, at least in my experience), then you'll have to resort to something involving the initial test of key.label === 'x' && key.name === 122

FZs Over a year ago

Oh, how good will it be when Records (currently Stage 2) come out! They would solve all these kinds of problems...

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