That's part of the task:

Your task is to find out what this is and write a function that will add atwo strings together, there must be a space between the two strings.

It's not directly related to how + or concat work. Also, you can't use them here.

Looks like I did saw all this "...there must be a space between the two strings"

And where does it say it adds a space?

Theres an error on the task description because str1 + str2 returns a string without space between them

I forgot that, even doing it just to assign it to another var, it was mutating it :/
Thanks

You've destroyed games with splice how is that not mutating the input?

No, I'm not mutating the input

Write console.log(games); as the first line of your code and before your function's return line too, see if they're different, if so, you've mutated the input.

Could you just post your code in a comment with a spoiler tag?

What do you mean with 'mutating the input'?
It's changing the initial value?
If it's that, I'm not mutating.

Note: I'm doing with javascript.
My function it's always expecting that the value sent it's an valid array

The user can modify the input in Python.

But have you tried not mutating the input?

Hi,

No and I think there's an issue with the tests when we try to submit, because all of them are saying that the expected result is zero.
On the sample tests the code, are working fine.
For what I saw now, on the tests that runs on the submission, it's passing an invalid array

Ex:
Testing for points(['1:0','2:0','3:0','4:0','2:1','3:1','4:1','3:2','4:2','4:3'])
Test Passed: Value == 30

Testing for games = [1:4,1:3,2:0,0:2,4:3,4:1,1:1,3:4,1:3,1:3] =
It should work for random inputs too - Expected: 0, instead got: 10