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158

TypeScript - How to use array map to an ES 6 Map?

rated 0 times [ 161] [ 3] / answers: 1 / hits: 16859 / 6 Years ago, tue, november 27, 2018, 12:00:00

Lets say I have an array of key value objects:

const data = [

    {key: object1, value: data1},

    {key: object2, value: data2},

    {key: object3, value: data3},

]



const mappedData = data.map(x => [x.key, x.value]);



const ES6Map = new Map<string, string>(mappedData.values())

How do I convert it to ES 6 map? It works in JavaScript but TypeScript will complain. Here I got the error of Argument of type 'IterableIterator<string[]>' is not assignable to parameter of type 'ReadonlyArray<[string, string]>'. Property 'length' is missing in type 'IterableIterator<string[]>'.

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answered 6 Years ago meliashelbief · Accepted Answer

You need to do type assertion and tell typescript that your mappedData is of type Array<[string,string]> instead of string[][] which is a sub type for Array<[any,any]> as needed by Map constructor.

Do

const mappedData = data.map(x => [x.key, x.value] as [string, string]);

instead of

const mappedData = data.map(x => [x.key, x.value]);

and also

drop the values() call as pointed out in comments.