ES7 Map JSON introduces a new feature by using square brackets

Question

ES7 Map JSON introduces a new feature by using square brackets

Currently, I am utilizing core-js for the Map collection because it appears that ES7 Map includes a Map to JSON feature that is absent in ES6 Map.

(ES6): JSON.stringify(new Map().set('myKey1', 'val123').set('myKey2', 'val456')); => {}

However, ES 7 seems to introduce unnecessary square brackets to the key value pairs

For example (ES7): JSON.stringify(new Map().set('myKey1', 'val123').set('myKey2', 'val456')); => [["myKey1","val123"],["myKey2","val456"]]

where I was expecting something like this:

{"myKey1": "val123","myKey2":"val456"}

Any assistance would be greatly appreciated!

EDIT: Upon closer inspection, I realized there was a mistake in the JSON I provided, but that was simply a typo made while posting the question.

Essentially, I am using TypeScript to create a new Map containing string key-value pairs like

new Map<string, string>()

I am anticipating the JSON output of such a Map to be

{"myKey1": "val123","myKey2":"val456"}

and would appreciate any suggestions on how to achieve this desired result.

javascript json typescript ecmascript-6 ecmascript-2016

Answer 1

Answer №1

The reason for this is that the default map iterator is .entries which generates key-value pairs. If you wish to utilize a different iterator, you will need to define or implement it, like so:

function *transformedEntries(map) {
    for (let [k, v] of map) {
        yield k;
        yield v;
    }
}


let m = new Map().set('key1', 'value1').set('key2', 'value2');
let result = JSON.stringify([...transformedEntries(m)]);

console.log(result)

Answer 2

The reason for this is that the default map iterator is .entries which generates key-value pairs. If you wish to utilize a different iterator, you will need to define or implement it, like so:

function *transformedEntries(map) {
    for (let [k, v] of map) {
        yield k;
        yield v;
    }
}


let m = new Map().set('key1', 'value1').set('key2', 'value2');
let result = JSON.stringify([...transformedEntries(m)]);

console.log(result)

ES7 Map JSON introduces a new feature by using square brackets

Answer №1

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