Typescript: Map string[] to [string, string]

Question

How do I map an string array string[] to a 2 dimensional array with strings [string, string]?

I tried

const animals: string[] = ['Dog', 'Cat', 'Mouse'];
// This throws an error
let splittedArray: [string, string] = animals.slice(0,2);

// This doesn't throw an error
// let splittedArray: [string, string] = ['Dog', 'Cat'];

// Error Message
// Type 'string[]' is missing the following properties from type '[string, string]': 0, 1 ts(2739)

My desired output should be:

console.log(splittedArray);
// ['Dog', 'Cat']

What you tried is not an 2D array of strings; it is a array with 2 elements of type string — Volper
– Volper, Commented Dec 6, 2019 at 12:25
I know, it is just an example. I really need an array with exactly 2 elements of type string. — Ling Vu
– Ling Vu, Commented Dec 6, 2019 at 12:26
you need animals.slice(0, 2)... 0, 1 would give you just ['Dog'] — tanmay
– tanmay, Commented Dec 6, 2019 at 12:28
Still: Type 'string[]' is missing the following properties from type '[string, string]': 0, 1 — Ling Vu
– Ling Vu, Commented Dec 6, 2019 at 12:29

Gaurang Dhorda · Accepted Answer · 2019-12-06 12:57:32Z

1

just change type declaration to this... The as operator's mostly designed for *.tsx files to avoid the syntax ambiguity. Working StackBlitz Link is

const animals: string[] = ['Dog', 'Cat', 'Mouse'];
let splittedArray = animals.slice(0,2) as [string,string];
console.log(splittedArray)

answered Dec 6, 2019 at 12:57

Gaurang Dhorda

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1 Comment

Ling Vu Over a year ago

It works, perfect. Thank you! Still don't know what this cryptic error message means, but anyways. At least a solution for now

Layera · Accepted Answer · 2019-12-06 12:50:27Z

1

Do you want a 2D array or an array with 2 elements? This seems to work for your output:

    const animals: string[] = ['Dog', 'Cat', 'Mouse'];
    let splittedArray: string[] = animals.slice(0,2);

edited Dec 6, 2019 at 12:50

answered Dec 6, 2019 at 12:45

Layera

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4 Comments

Ling Vu Over a year ago

I want an array with exactly 2 elements. [string, string]

Layera Over a year ago

Then my answer till work it will give you the output of : ['Dog', 'Cat']

Ling Vu Over a year ago

That's what my question is about. I know how to extract 2 elements from an array. My question is to set the value of an array to an array with [string, string]

Layera Over a year ago

Why the downvote? the reason for your error message is because animals.slice(0,2) is of type String[]. You can not write [string, string]. If you splice at index 0 with 2 element you get an array with 2 elements, starting from index 0. Is that not what you want?

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