Method sumBy returns string

[ekabolotina]

There are cases when method sumBy could return string instead of number.

Current behavior:

_.sumBy([{ a: 1 }, { a: 'f' }, { a: null }], 'a'); // '1fnull'

Returned value is of type string.

Expected behavior:

_.sumBy([{ a: 1 }, { a: 'f' }, { a: null }], 'a'); // NaN

Returned value is of type number.

[katsanva]

Lets see how JS behaves in this case:

> 1 + 'f' + null
"1fnull"

So Lodash is doing things right!

If you actually do want to have NaN for some reason, you should use Number(_.sumBy([{ a: 1 }, { a: 'f' }, { a: null }], 'a')) which equals to Number("1fnull") and evaluates to NaN

[AmanAmbasta]

Well according to the function definition, it should return number

[arnavpanwar99]

@AmanAmbasta NaN is also a number, so according to function definition its correct as well.

[Trott]

@AmanAmbasta NaN is also a number, so according to function definition its correct as well.

It's not returning NaN. It's returning a string. That's the whole point of this bug report.

_.sumBy([{ a: 1 }, { a: 'f' }, { a: null }], 'a'); // '1fnull'