Typescript problem to loop through an array of tuple and get specific values

Question

I have to write a function that takes an array of tuples, each tuple consists of a name and an age. The function should return only the names.

So I wrote it like this:

type someTuple = [string, number]

function names(namesAndAges: someTuple[]) {
  let allNames: string[]
  allNames.push(namesAndAges.forEach( nameAndAge => nameAndAge[0]))
  
  return allNames
}

When I call it with this:

names([['Amir', 34], ['Betty', 17]]);

I get this error:

type error: type error: Variable 'allNames' is used before being assigned.

Can anyone point what is wrong with this code?

b3hr4d · Accepted Answer · 2021-01-16 12:00:16Z

1

You didn't declare allNames to be an array, so change it to this:

let allNames: string[] = []

If you want to get all name in an array your function should be like this:

type someTuple = [string, number]

function names(namesAndAges: someTuple[]) {
  let allNames: string[] = []
  namesAndAges.forEach( nameAndAge => 
    allNames.push(nameAndAge[0])
  )
  return allNames
}

names([['Amir', 34], ['Betty', 17]]);

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edited Jan 16, 2021 at 12:00

answered Jan 16, 2021 at 11:45

b3hr4d

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3 Comments

Allan Over a year ago

Thank you, I was forgetting this. Now I'm getting this error: type error: Argument of type 'void' is not assignable to parameter of type 'string'

Allan Over a year ago

Perfect! Thank you!

b3hr4d Over a year ago

Happy to help you :)

fralps · Accepted Answer · 2022-08-31 10:29:32Z

0

You can also use .map here for a better code readability

function names(namesAndAges: [string, number][]): string[] {
  return namesAndAges.map(nameAndAge => nameAndAge[0]);
}

names([['Amir', 34], ['Betty', 17]]);

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answered Aug 31, 2022 at 10:29

fralps

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