TypeScript: How to dynamically set properties on objects?

Question

I want to convert a Typescript Map to an object. The following code shows a compiler error:

const sourceMap = new Map<string, string>();
sourceMap.set('foo', 'bar');

const jsonObject = {};
sourceMap.forEach((value, key) => {
    jsonObject[key] = value;
});
console.log(JSON.stringify(jsonObject));

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The compiler doesn't like the line jsonObject[key] = value; saying:

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{}'. No index signature with a parameter of type 'string' was found on type '{}'.(7053)

How can I fix that or what am I doing wrong here?

Titian Cernicova-Dragomir · Accepted Answer · 2020-05-07 09:53:05Z

2

You can add an explicit type annotation to jsonObject to allow indexing with any string. The predefined type Record should work fine:

const sourceMap = new Map<string, string>();
sourceMap.set('foo', 'bar');

const jsonObject: Record<string, string> = {};
sourceMap.forEach((value, key) => {
    jsonObject[key] = value;
});
console.log(JSON.stringify(jsonObject));

Playground Link

answered May 7, 2020 at 9:53

Titian Cernicova-Dragomir

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