typescript error - 'boolean' is not assignable to type 'number'

Question

Can anybody help me.

I am trying to sort strings from array

var someArray= ["3a445a_V1", "3", "2a33s454_V1", "1", "3_V2", "2s4a34s3_V2", "234343"];

const [record] = someArray.map(r => parseFloat(r.replace('_V','.'))).sort((a,b) => a < b);

console.log(record)
//it returns 3a445a.1

JFIDDLE

In browser console.log it works fine, not in typescript?

typescript it is giving below error Error:

error TS2345: Argument of type '(a: number, b: number) => boolean' is not 
assignable to parameter of type '(a: number, b: number) => number'.
      Type 'boolean' is not assignable to type 'number'.

Any idea? thanks in advance

(a,b) => a < b is not a valid comparison function. As typescript says, it's supposed to return a number, not a boolean. — melpomene
– melpomene, Commented Feb 11, 2018 at 14:20
"In browser console.log it works fine' It doesn't, actually, it just happens that your data don't reveal the problems with it. — T.J. Crowder
– T.J. Crowder, Commented Feb 11, 2018 at 14:20
@T.J. Crowder , i have just created fiddle, please check and guide me — Manjunath Siddappa
– Manjunath Siddappa, Commented Feb 11, 2018 at 14:23

2 revs · Accepted Answer · 2021-09-14 06:33:38Z

19

.sort((a,b) => a < b) is incorrect. The TypeScript message is right: The sort callback should return a number, not a boolean.

Instead: .sort((a,b) => a - b) (- instead of <). Or b - a to sort the other way. This is because the sort callback should return a negative number if a comes before b, 0 if their order doesn't matter, and a positive number if b comes before a. Since you seem to want ascending order, that's a - b so that if a is less than b, it returns a negative number, etc. b - a does a descending sort.

edited Sep 14, 2021 at 6:33

community wiki

2 revs
T.J. Crowder

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1 Comment

Ray Over a year ago

Thank you, didn't know that I could just write b - a!

Procrastinator · Accepted Answer · 2022-03-02 07:50:14Z

0

you can also use .sort((a,b) => Number(a>b)). This worked for me just fine.

edited Mar 2, 2022 at 7:50

Procrastinator

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answered Feb 24, 2022 at 19:54

Ashiq Ali

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